Apparatuses and methods for digital subcarrier parameter modifications for optical communication networks

ABSTRACT

Optical network systems are disclosed, including systems having transmitters with a digital signal processor comprising forward error correction circuitry that provides encoded first electrical signals based on input data; and power adjusting circuitry that receives second electrical signals indicative of the first electrical signals, the power adjusting circuitry supplying third electrical signals, wherein each of the third electrical signals is indicative of an optical power level of a corresponding to one of a plurality of optical subcarriers output from an optical transmitter.

INCORPORATION BY REFERENCE

The entirety of the following patents and patent applications are herebyexpressly incorporated herein by reference: U.S. Pat. No. 8,831,439,entitled “Upsampling Optical Transmitter”, which issued Sep. 9, 2014;U.S. Pat. No. 10,014,975, entitled “Channel Carrying Multiple DigitalSubcarriers”, which issued Jul. 3, 2018; U.S. patent application Ser.No. 16/155,624, entitled “Individually Routable Digital Subcarriers”,which was filed Oct. 9, 2018; U.S. Provisional Patent Application No.62/627,712, entitled “Independently Routable Digital Subcarriers forOptical Network”, which was filed Feb. 7, 2018; Provisional PatentApplication No. 62/668,297, entitled “Spectral Efficiency Improvementsusing Variable Subcarrier Root-Raised Cosine Shaping”, which was filedMay 8, 2018, to which the present application claims priority; andProvisional Patent Application No. 62/657,066, entitled “SubcarrierParameter Modification To Compensate For Legacy Optical FilterImpairments”, which was filed Apr. 13, 2018, to which the presentapplication claims priority.

FIELD OF THE DISCLOSURE

The disclosure generally relates to methods and apparatuses for thegeneration and use of subcarriers in optical communication systems. Moreparticularly the disclosure relates to such methods and apparatuses thatroute or direct individual subcarriers to a different destination,wherein the parameters of the subcarriers may be modified individuallybased on receiver characteristics and/or in accordance with the path orroute, including apparatuses, over which a corresponding subcarrier istransmitted.

BACKGROUND

Communication systems are known in which optical signals, each beingmodulated to carry data and having a different wavelength, aretransmitted from a first location to a second location. The opticalsignals may be combined on a single fiber and transmitted to a receivingnode that includes circuitry to optically separate or demultiplex eachsignal. Alternatively, coherent detection techniques may be employed toextract the data carried by each optical signal.

In such systems, a plurality of transmitters may be provided, such thateach transmitter supplies a respective one of the optical signals.Typically, each transmitter includes a laser, modulator, and associatedcircuitry for controlling the modulator and the laser. As networkcapacity requirements increase, however, additional transmitters may beprovided to supply additional optical signals, but at significantlyincreased cost.

Moreover, communications systems may include multiple nodes, such thatselected optical signals may be intended to transmission to certainnodes, and other signals may be intended for reception by one or moreother nodes. Accordingly, optical add-drop multiplexers (“OADMs”) may beprovided to drop one or more signals at an intended local receiver, forexample, while other optical signals are passed by the OADM to one ormore downstream nodes. Further, optical signals may be added by the OADMfor transmission to one or more nodes in the communication system. Thus,the optical signals may be transmitted over varying distances andthrough varying numbers of OADMs. In addition, the data and/or baudrate, and or modulation format is preferably tailored to a particularroute, as well as the capacity of the intended receiver.

Thus, not only may multiple transmitters be required to provide arequired number of optical signals to satisfy network capacity needs,but each transmitter may be required to be customized to generate eachoptical signal with a desired modulation format, data rate, and/or baudrate.

The required power for a subcarrier to reach its destination at adesired power may vary depending on the transmission of the subcarrierthrough a particular route in the optical network. For example, theroutes may contain a varied number of fiber splitters, power combiners,filters, and other components common in DWDM deployment scenarios,and/or the routes may be of different lengths. Further, some legacyOptical Power Monitoring algorithms may expect a specific carrier shapeassociated with older DWDM optical transmission technologies. Therefore,methods and systems are needed to control the parameters of subcarriersin a carrier in order to satisfy destination requirements in opticalcommunication networks. Additionally, feedback may be sent between endsof an optical communication network system based on measures ofperformance.

SUMMARY

Optical communication network systems and methods are disclosed. Theproblem of requiring multiple transmitters to provide a required numberof optical signals to satisfy network capacity needs, and requiring eachtransmitter to be customized to generate each optical signal with adesired power, modulation format, data rate, and/or baud rate isaddressed through systems and methods for providing subcarriers that maybe routed through a network independently of one another. In addition,each subcarrier may have characteristics, such as optical power level,baud rate, data rate and modulation format, spectral width, and/orfrequency spacings that may be tailored based on the intended receiverfor such subcarrier and the particular optical path or route and/orapparatuses over/through which the subcarrier is transmitted.

Consistent with an aspect of the present disclosure, a digital signalprocessor may comprise forward error correction circuitry that providesencoded first electrical signals based on input data; and poweradjusting circuitry that receives second electrical signals indicativeof the first electrical signals, the power adjusting circuitry supplyingthird electrical signals, wherein each of the third electrical signalscorresponds to an optical power level of a corresponding to one of aplurality of optical subcarriers output from an optical transmitter. Inone implementation, each of the third electrical signals may have anassociated one of a plurality of bandwidths, each of which maycorrespond to a spectral width of a respective one of the plurality ofoptical subcarriers.

Consistent with an aspect of the present disclosure, the power adjustingcircuitry may comprise a plurality of digital multipliers correspondingto a plurality of independent data streams. The plurality of digitalmultipliers may be adjustable based on one or more control signal suchthat power adjustment of each of the third electrical signals isconfigurable.

Consistent with an aspect of the present disclosure, the power adjustingcircuitry is adjustable based on one or more fourth electrical signalsprovided by a receiver that detects one or more of the plurality ofoptical subcarriers output from the optical transmitter. The one or morefourth electrical signals may be based on an optical power level of theone or more of the plurality of optical subcarriers previously detectedby the receiver. The one or more fourth electrical signals may be basedon a target optical power level of the one or more of the plurality ofoptical subcarriers at the receiver. The one or more fourth electricalsignals may be associated with a feedback optical signal sent from thereceiver to the optical transmitter.

Consistent with an aspect of the present disclosure, a node may comprisea transmitter, which may comprise a digital signal processor an opticaltransmitter comprising a digital signal processor, comprising: forwarderror correction circuitry that provides encoded first electricalsignals based on input data; and power adjusting circuitry that receivessecond electrical signals indicative of the first electrical signals,the power adjusting circuitry supplying third electrical signals,wherein each of the third electrical signals corresponds to an opticalpower level of a corresponding one of a plurality of optical subcarriersoutput from the optical transmitter. The node may further comprise acontrol circuit that receives fourth electrical signals indicative ofreceived power level of one or more of the plurality of opticalsubcarriers, provided by a receiver that detects one or more of theplurality of optical subcarriers output from the optical transmitter,whereby the control circuit adjusts the power adjusting circuitry basedon the received fourth electrical signals.

Consistent with an aspect of the present disclosure, the node mayfurther comprise a demultiplexer that filters an optical feedback signalprovided by the receiver on an Optical Service Channel; and a photodiodethat coverts the optical feedback signal from the demultiplexer into thefourth electrical signals and forwards the fourth electrical signals tothe control circuit.

Consistent with an aspect of the present disclosure, the node mayfurther comprise a filter that filters an optical sideband signalprovided by the receiver on a Control Channel having a lower frequencythan the frequency of the plurality of optical subcarriers to generatethe fourth electrical signals.

Consistent with an aspect of the present disclosure, the fourthelectrical signals may be generated from an optical feedback signal fromthe receiver, the optical feedback signal carrying a frame, the framehaving a header that includes data, and wherein the optical power levelsof the optical subcarriers are based on the data.

Consistent with an aspect of the present disclosure, a transmitter maycomprise a digital signal processor receiving a plurality of independentdata streams, the digital signal processor supplying outputs based onthe plurality of independent data streams, the outputs including a firstdigital subcarrier having a first frequency bandwidth and a seconddigital subcarrier having a second frequency bandwidth different thanthe first frequency bandwidth; one or more digital-to-analog converterconfigured to convert the outputs of the digital signal processor tovoltage signal outputs; a laser configured to output an optical lightbeam; and a modulator configured to modulate the optical light beam,based on the voltage signal outputs, to output a modulated opticalsignal including a plurality of optical subcarriers based on the outputsof the digital signal processor, wherein a first one of the plurality ofoptical subcarriers carries data indicative of a first one of theplurality of independent data streams, and a second one of the pluralityof optical subcarriers carries data indicative of a second one of theplurality of independent data streams, wherein the first one of theplurality of optical subcarriers has a first optical bandwidth and thesecond one of the plurality of optical subcarriers has a second opticalbandwidth different than the first optical bandwidth, and the first oneof the plurality of optical subcarriers has a first level of opticalpower and the second one of the plurality of optical subcarriers has asecond level of optical power different than the first level of opticalpower. Consistent with an aspect of the present disclosure, the digitalsignal processor may comprises a plurality of digital multiplierscorresponding to the plurality of independent data streams, theplurality of digital multipliers supplying electrical signals such thatthe power levels of the optical subcarriers are based on the electricalsignals output from the plurality of digital multipliers. The pluralityof digital multipliers may be adjustable based on one or more controlsignal such that power adjustment is configurable for any of the firstand second digital subcarrier.

Consistent with an aspect of the present disclosure, an optical networksystem may comprise a hub, comprising: a transmitter, comprising: adigital signal processor receiving a plurality of independent datastreams, the digital signal processor supplying outputs based on theplurality of independent data streams, the outputs including a firstdigital subcarrier having a first frequency bandwidth and a seconddigital subcarrier having a second frequency bandwidth different thanthe first frequency bandwidth; one or more digital-to-analog converterconfigured to convert the outputs of the digital signal processor tovoltage signal outputs; a laser configured to output an optical lightbeam; and a modulator configured to modulate the optical light beam,based on the voltage signal outputs, to output a modulated opticalsignal including a plurality of optical subcarriers based on the outputsof the digital signal processor, wherein a first one of the plurality ofoptical subcarriers carries data indicative of a first one of theplurality of independent data streams, and a second one of the pluralityof optical subcarriers carries data indicative of a second one of theplurality of independent data streams, wherein the first one of theplurality of optical subcarriers has a first optical bandwidth and thesecond one of the plurality of optical subcarriers has a second opticalbandwidth different than the first optical bandwidth, and the first oneof the plurality of optical subcarriers has a first level of opticalpower and the second one of the plurality of optical subcarriers has asecond level of optical power different than the first level of power.The optical network system may further comprise a first edge nodecomprising a receiver configured to receive one or more of the pluralityof optical subcarriers; a second edge node comprising a receiverconfigured to receive one or more of the plurality of opticalsubcarriers; a first transmission path between the hub and the firstedge node; and a second transmission path between the hub and the secondedge node, wherein the second transmission path differs from the firsttransmission path. The first level of power of the first opticalsubcarrier and the second level of power of the second opticalsubcarrier may be based at least in part on one or more characteristicsof at least one of the first transmission path and the secondtransmission path. The digital signal processor may comprise a pluralityof digital multipliers corresponding to the plurality of independentdata streams, the plurality of digital multipliers supplying electricalsignals such that the optical power levels of the optical subcarriersare based on the electrical signals output from the plurality of digitalmultipliers.

Consistent with an aspect of the present disclosure, an optical networksystem, may comprise two or more edge nodes, each edge node comprising:a transmitter, comprising a digital signal processor receiving aplurality of independent data streams, the digital signal processorsupplying outputs based on the plurality of independent data streams,the outputs including a first digital subcarrier having a firstfrequency bandwidth and a second digital subcarrier having a secondfrequency bandwidth different than the first frequency bandwidth; one ormore digital-to-analog converter configured to convert the outputs ofthe digital signal processor to voltage signal outputs; a laserconfigured to output an optical light beam; and a modulator configuredto modulate the optical light beam, based on the voltage signal outputs,to output a modulated optical signal including a plurality of opticalsubcarriers based on the outputs of the digital signal processor,wherein a first one of the plurality of optical subcarriers carries dataindicative of a first one of the plurality of independent data streams,and a second one of the plurality of optical subcarriers carries dataindicative of a second one of the plurality of independent data streams,wherein the first one of the plurality of optical subcarriers has afirst optical bandwidth and the second one of the plurality of opticalsubcarriers has a second optical bandwidth different than the firstoptical bandwidth, and the first one of the plurality of opticalsubcarriers has a first level of optical power and the second one of theplurality of optical subcarriers has a second level of optical powerdifferent than the first level of optical power.

The optical network system may further comprise a hub comprising: areceiver configured to receive one or more of the plurality of opticalsubcarriers; and a transmitter; a first transmission path between afirst one of the two or more edge nodes and the hub; and a secondtransmission path between a second one of the two or more edge nodes andthe hub, wherein the second transmission path differs from the firsttransmission path. The first level of optical power of the first opticalsubcarrier and the second level of optical power of the second opticalsubcarrier may based at least in part on one or more characteristics ofat least one of the first transmission path and the second transmissionpath.

The digital signal processor may comprise a plurality of digitalmultipliers corresponding to the plurality of independent data streams,the plurality of digital multipliers configured to control power gain ofthe optical subcarriers. The plurality of digital multipliers may beconfigured to control power gain of the optical subcarriers based atleast in part on one or more characteristics of at least one of thefirst transmission path and the second transmission path.

Consistent with as aspect of the present disclosure, the hub may beconfigured to transmit from the transmitter of the hub informationindicative of one or more measurements of the one or more of theplurality of optical subcarriers to one or more of the two or more edgenodes, and wherein the edge nodes are configured to adjust one or moreof the first level of optical power of the first optical subcarrier andthe second level of optical power of the second optical subcarrier basedon the transmitted information. The information indicative of one ormore measurements of the one or more of the plurality of opticalsubcarriers may be associated with a feedback optical signal sent fromthe transmitter of the hub to the one or more edge node. The feedbackoptical signal may be transmitted on an Optical Service Channel. Thefeedback optical signal may be transmitted on a Control Channel having alower frequency than the frequency of the plurality of opticalsubcarriers. The feedback optical signal may carry a frame, the framehaving a header that includes data, and the optical power levels of oneor more of the plurality of the optical subcarriers may be based on thedata.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate one or more implementationsdescribed herein and, together with the description, explain theseimplementations. In the drawings:

FIG. 1 illustrates an optical communication system consistent with anaspect of the present disclosure;

FIG. 2 is a diagram illustrating an example of components of an opticaltransmitter shown in FIG. 1;

FIG. 3 is a diagram illustrating example components of an exemplarytransmitter digital signal processor (Tx DSP) shown in FIG. 2;

FIG. 4A illustrates an exemplary plurality of subcarriers consistentwith an aspect of the present disclosure;

FIG. 4B illustrates another exemplary plurality of subcarriersconsistent with an aspect of the present disclosure;

FIG. 4C illustrates another exemplary plurality of subcarriersconsistent with an aspect of the present disclosure;

FIG. 4D illustrates another exemplary plurality of subcarriersconsistent with an aspect of the present disclosure;

FIG. 4E illustrates another exemplary plurality of subcarriersconsistent with an aspect of the present disclosure;

FIG. 5A is a diagram illustrating a portion of an exemplary processconsistent with an aspect of the present disclosure;

FIG. 5B is a diagram illustrating a portion of another exemplary processconsistent with an aspect of the present disclosure;

FIG. 5C is a diagram illustrating exemplary variable-spaced subcarriersconsistent with an aspect of the present disclosure;

FIG. 5D is a diagram illustrating exemplary variable-spaced subcarriersconsistent with an aspect of the present disclosure;

FIG. 5E is a diagram illustrating an exemplary subcarrier consistentwith an aspect of the present disclosure;

FIG. 6 is a diagram illustrating an example of components of an opticalreceiver shown in FIG. 1 consistent with an aspect of the presentdisclosure;

FIG. 7 is a diagram illustrating example components of an exemplaryreceiver digital signal processor (Rx DSP), such as that shown in FIG.6, consistent with an aspect of the present disclosure;

FIG. 8A is an illustration of a use case example of subcarriers havingfixed subcarrier width and variable capacity per subcarrier consistentwith an aspect of the present disclosure;

FIG. 8B is an illustration of another use case example of subcarriershaving fixed subcarrier width and variable capacity per subcarrierconsistent with an aspect of the present disclosure;

FIG. 8C is an illustration of another use case example of subcarriershaving fixed subcarrier width and variable capacity per subcarrierconsistent with an aspect of the present disclosure;

FIG. 8D is an illustration of another use case example of subcarriershaving fixed subcarrier width and variable capacity per subcarrierconsistent with an aspect of the present disclosure;

FIG. 8E is an illustration of another use case example of subcarriershaving fixed subcarrier width and variable capacity per subcarrierconsistent with an aspect of the present disclosure;

FIG. 8F is an illustration of another use case example of subcarriershaving fixed subcarrier width and variable capacity per subcarrierconsistent with an aspect of the present disclosure;

FIG. 8G is an illustration of another use case example of subcarriershaving fixed subcarrier width and variable capacity per subcarrierconsistent with an aspect of the present disclosure;

FIG. 9A is an illustration of a use case example of subcarriers havingfixed capacity and variable subcarrier width consistent with an aspectof the present disclosure;

FIG. 9B is an illustration of another use case example of subcarriershaving fixed capacity and variable subcarrier width consistent with anaspect of the present disclosure;

FIG. 9C is an illustration of another use case example of subcarriershaving fixed capacity and variable subcarrier width consistent with anaspect of the present disclosure;

FIG. 9D is an illustration of another use case example of subcarriershaving fixed capacity and variable subcarrier width consistent with anaspect of the present disclosure;

FIG. 10 illustrates an exemplary mesh network configuration consistentwith a further aspect of the present disclosure;

FIG. 11A illustrates an exemplary ring network configuration consistentwith a further aspect of the present disclosure;

FIG. 11B illustrates exemplary components of a node of the network ofFIG. 11A consistent with a further aspect of the present disclosure;

FIG. 12A illustrates an exemplary network configuration consistent witha further aspect of the present disclosure;

FIG. 12B illustrates another exemplary network configuration consistentwith a further aspect of the present disclosure;

FIG. 13 illustrates an exemplary ring and hub network configurationconsistent with a further aspect of the present disclosure;

FIG. 14 is a diagram illustrating example components of an exemplarydigital signal processor of a transmitter having a digital multiplierconsistent with a further aspect of the present disclosure;

FIG. 15 is a diagram illustrating example components of anotherexemplary transmitter digital signal processor (Tx DSP) consistent witha further aspect of the present disclosure;

FIG. 16 is a diagram illustrating example components of anotherexemplary transmitter digital signal processor (Tx DSP) consistent witha further aspect of the present disclosure;

FIG. 17 is a diagram illustrating example components of anotherexemplary transmitter digital signal processor (Tx DSP) consistent witha further aspect of the present disclosure;

FIG. 18 illustrates an exemplary legacy optical carrier;

FIG. 19 illustrates an exemplary coherent carrier consistent with anaspect of the present disclosure;

FIG. 20 illustrates another exemplary coherent carrier consistent with afurther aspect of the present disclosure;

FIG. 21 is a diagram illustrating example components of an exemplaryoptical network transmitting subcarriers from a hub and receivingsubcarriers at edge nodes;

FIG. 22 is a diagram illustrating example components of an exemplaryoptical network transmitting subcarriers from a hub and receivingsubcarriers at edge nodes;

FIG. 23 is a diagram illustrating example components of an exemplaryoptical network transmitting subcarriers from edge nodes and receivingsubcarriers at a hub;

FIG. 24A is a diagram illustrating example components of an exemplaryoptical network transmitting subcarriers from edge nodes and receivingsubcarriers at a hub;

FIG. 24B is a diagram illustrating example components of anotherexemplary optical network transmitting subcarriers from edge nodes andreceiving subcarriers at a hub;

FIG. 25 is a diagram illustrating example components of an exemplaryoptical network transmitting subcarriers from an edge node and receivingsubcarriers at a hub through multiple transmission paths;

FIG. 26 is a diagram illustrating example components of an exemplaryoptical network transmitting subcarriers from an edge node and receivingsubcarriers at a hub through multiple transmission paths;

FIG. 27 is a diagram illustrating components of another exemplaryoptical network consistent with an aspect of the present disclosure;

FIG. 28 is a diagram illustrating components of a node consistent withan aspect of the present disclosure;

FIG. 29 is an exemplary frequency graph of carriers transmitted from thenode of FIG. 28;

FIG. 30 is an illustration of the data structure of an exemplary opticalsignal consistent with an aspect of the present disclosure;

FIG. 31A is a diagram illustrating example components of an exemplaryreceiver consistent with an aspect of the present disclosure;

FIG. 31B is a diagram illustrating example components of anotherexemplary receiver digital signal processor (Rx DSP), such as that shownin FIG. 6, consistent with an aspect of the present disclosure.

DETAILED DESCRIPTION

The following detailed description refers to the accompanying drawings.The same reference numbers in different drawings may identify the sameor similar elements.

The mechanisms proposed in this disclosure circumvent the problemsdescribed above. The present disclosure describes a system methods andapparatuses that route or direct individual subcarriers to a differentdestination, wherein the modulation format, data rate, and/or baud rate,as well as the spectral width and frequency spacing between subcarriers,may be tailored for each subcarrier based on receiver characteristicsand/or in accordance with the path or route over which a correspondingsubcarrier is transmitted.

Definitions

If used throughout the description and the drawings, the following shortterms have the following meanings unless otherwise stated:

ADC stands for analog-to-digital converter.

DAC stands for digital-to-analog converter.

DSP stands for digital signal processor.

OADM stands for optical add-drop multiplexer.

PIC stands for photonic integrated circuit.

Q stands for a measure of performance and represents the systemtolerance in dB of an optical subcarrier.

Rx (or RX) stands for Receiver, which typically refers to opticalchannel receivers, but can also refer to circuit receivers.

Tx (or TX) stands for Transmitter, which typically refers to opticalchannel transmitters, but can also refer to circuit transmitters.

Description

As used herein, the terms “comprises,” “comprising,” “includes,”“including,” “has,” “having” or any other variation thereof, areintended to cover a non-exclusive inclusion. For example, a process,method, article, or apparatus that comprises a list of elements is notnecessarily limited to only those elements but may include otherelements not expressly listed or inherent to such process, method,article, or apparatus. Further, unless expressly stated to the contrary,“or” refers to an inclusive or and not to an exclusive or. For example,a condition A or B is satisfied by anyone of the following: A is true(or present) and B is false (or not present), A is false (or notpresent) and B is true (or present), and both A and B are true (orpresent).

In addition, use of the “a” or “an” are employed to describe elementsand components of the embodiments herein. This is done merely forconvenience and to give a general sense of the inventive concept. Thisdescription should be read to include one or more and the singular alsoincludes the plural unless it is obvious that it is meant otherwise.

Further, use of the term “plurality” is meant to convey “more than one”unless expressly stated to the contrary.

Further, the phrase “based on” is intended to mean “based, at least inpart, on” unless explicitly stated otherwise.

Also, certain portions of the implementations have been described as“components” or “circuitry” that perform one or more functions. The term“component” or “circuitry” may include hardware, such as a processor, anapplication specific integrated circuit (ASIC), or a field programmablegate array (FPGA), or a combination of hardware and software. Softwareincludes one or more computer executable instructions that when executedby one or more component cause the component or circuitry to perform aspecified function. It should be understood that the algorithmsdescribed herein are stored on one or more non-transient memory.Exemplary non-transient memory includes random access memory, read onlymemory, flash memory or the like. Such non-transient memory can beelectrically based or optically based. Further, the messages describedherein may be generated by the components and result in various physicaltransformations.

Finally, as used herein any reference to “one embodiment” or “anembodiment” or “implementation: means that a particular element,feature, structure, or characteristic described in connection with theembodiment or implementation is included in at least one embodiment orimplementation. The appearances of the phrase “in one embodiment” or “inone implementation” in various places in the specification are notnecessarily all referring to the same embodiment or implementation.

In accordance with the present disclosure, messages or data transmittedbetween nodes may be processed by circuitry within the inputinterface(s), and/or the output interface(s) and/or the control module.Circuitry could be analog and/or digital, components, or one or moresuitably programmed microprocessors and associated hardware andsoftware, or hardwired logic. Also, certain portions of theimplementations have been described as “components” that perform one ormore functions. The term “component,” may include hardware, such as aprocessor, an application specific integrated circuit (ASIC), or a fieldprogrammable gate array (FPGA), or a combination of hardware andsoftware. Software includes one or more computer executable instructionsthat when executed by one or more component cause the component toperform a specified function. It should be understood that thealgorithms described herein are stored on one or more non-transientmemory. Exemplary non-transient memory includes random access memory,read only memory, flash memory or the like. Such non-transient memorycan be electrically based or optically based. Further, the messagesdescribed herein may be generated by the components and result invarious physical transformations.

Consistent with an aspect of the present disclosure, electrical signals(which may be referred to as digital subcarriers or simply subcarriers)are generated in a Digital Signal Processor based on independent inputdata streams. Drive signals are generated based on the digitalsubcarriers, and such drive signals are applied to an optical modulator,including, for example, a Mach-Zehnder modulator. The optical modulatormodulates light output from a laser based on the drive signals to supplyoptical subcarriers, each of which corresponding to a respective digitalsubcarrier. Each of the optical subcarriers may be routed separatelythrough a network and received by optical receivers provided atdifferent locations in an optical communications network, where at leastone of the optical subcarriers may be processed, and the input datastream associated with such optical subcarrier(s) is output. For thesake of convenience, optical subcarriers may simply be referred to assubcarriers.

Accordingly, instead of providing multiple transmitters, each beingassociated with a respective optical signal, one transmitter, having, inone example, a laser, may be provided that supplies multiplesubcarriers, one or more of which carries data that may be independentlyroutable to a corresponding receiver provided at a unique location.Thus, since fewer transmitters are required consistent with the presentdisclosure, system costs may be reduced.

Since the subcarriers may be transmitted over different transmissionpaths having different characteristics to receivers having differentcapacities or other properties, characteristics of each subcarriers maybe tuned or adjusted to provide optimal performance. For example, theoptical power level, the modulation format, data rate, and/or baud ratemay be selected for a given subcarrier based on a particular paththrough the network and/or capacity or bandwidth of the intendedreceiver. These parameters may be selected to be different for othersubcarriers that are transmitted over different paths to differentreceivers in the network. In one example, the modulation format may beselected from binary phase shift keying (BPSK), quadrature phase shiftkeying (QPSK), and m-quadrature amplitude modulation (m-QAM, where m isan integer).

Consistent with a further aspect of the present disclosure, efficientclock or phase recovery of a received signals may be made more efficientby sensing data or information associated with one subcarrier having aspectral width that is wider than other subcarriers associated with aparticular carrier.

FIG. 1 is a diagram of a simplified view of an optical network 200 inwhich systems and/or methods described herein may be implemented. In oneexample, optical network 200 may constitute part of a larger networkincluding multiple nodes arranged as a mesh or a ring, as discussed ingreater detail below. As illustrated in FIG. 1, the optical network 200may include a transmitter (Tx) module 210, and/or a receiver (Rx) module220. In some implementations, the transmitter module 210 may beoptically connected to the receiver module 220 via one or more link 230.Additionally, the link 230 may include one or more optical amplifiers240 that amplify an optical signal as the optical signal is transmittedover the link 230.

The transmitter module 210 may include a number of optical transmitters212-1 through 212-M (where M is greater than or equal to one),waveguides 214, and/or optical multiplexers 216. In someimplementations, the transmitter module 210 may include additionalcomponents, fewer components, different components, or differentlyarranged components.

Each optical transmitter 212 may receive data for one or more datainputs 352, each of which may include a plurality of client data streams352-1 to 352-4 discussed in greater detail below with reference to FIG.2. Based on a respective data input, each transmitter provides a carrierand an associated plurality of optical subcarriers. The carrier has awavelength equal to or substantially equal to the wavelength ofcontinuous wave (CW) light output from a laser (see FIG. 2) and eachsubcarrier may have a frequency or wavelength that is different than thecarrier wavelength. The transmitter 212 is described in greater detailbelow in relation to FIG. 2.

Remaining now with FIG. 1, in one implementation, the transmitter module210 may include 5, 10, or some other quantity of the opticaltransmitters 212. In one example, the carrier wavelength of the opticalsignals supplied by each transmitter 212 may be tuned to conform to awavelength grid, such as a standard grid published by theTelecommunication Standardization Sector (ITU-T). The carrierwavelengths may also be tuned to conform to a flexible grid in which thespacing between the carrier wavelengths is non-uniform. Moreover, thecarrier wavelengths may be tuned to be more tightly packed spectrally tocreate a super channel.

The waveguides 214 may include an optical link or some other link totransmit output optical signals (each including a carrier and aplurality of optical subcarriers) of the optical transmitters 212. Insome implementations, each optical transmitter 212 may include onewaveguide 214, or multiple waveguides 214, to transmit output opticalsignals of the optical transmitters 212 to the optical multiplexer 216.

The optical multiplexer 216 may include a power combiner, an arrayedwaveguide grating (AWG) or some other multiplexer device. In someimplementations, the optical multiplexer 216 may combine multiple outputoptical signals, associated with the optical transmitters 212, into asingle optical signal (e.g., a WDM signal). In some implementations, theoptical multiplexer 216 may combine multiple output optical signals,associated with the optical transmitters 212, in such a way as tocombine polarization multiplexed signals (e.g., also referred to hereinas a WDM signal). A corresponding waveguide may output the WDM signal onan optical fiber, such as the link 230. The optical multiplexer 216 mayinclude waveguides connected to an input and/or an output.

As further shown in FIG. 1, the optical multiplexer 216 may receiveoutput optical signals outputted by the optical transmitters 212, andoutput one or more WDM signals. Each WDM signal may include one or moreoptical signals, such that each optical signal includes one or morewavelengths. In some implementations, each optical signal in the WDMsignal may have a first polarization (e.g., a transverse magnetic (TM)polarization), and a second, substantially orthogonal polarization(e.g., a transverse electric (TE) polarization). Alternatively, eachoptical signal may have one polarization.

The link 230 may comprise an optical fiber. The link 230 may transportone or more optical signals. The amplifier 240 may include one or moreamplification device, such as a doped fiber amplifier and/or a Ramanamplifier. The amplifier 240 may amplify the optical signals as theoptical signals are transmitted via the link 230.

In addition, one or more OADMs 229 may be provided along the fiber link230. The OADMs 229 may be configured to add or drop one or more opticalsubcarriers included in the optical signals output from eachtransmitters. For example, as further shown in FIG. 1, opticalsubcarrier SC1 of a first optical signal may be added and/or dropped (asindicated by the arrows shown in FIG. 1) at OADM 229-1, and opticalsubcarrier SC2 of another optical signal may be added and/or dropped (asshown by the arrows in FIG. 1) at OADM 229-2.

The receiver module 220 may include optical demultiplexer 222,waveguides 224, and/or optical receivers 226-1 through 226-N (where N isgreater than or equal to one). In some implementations, the receivermodule 220 may include additional components, fewer components,different components, or differently arranged components.

The optical demultiplexer 222 may include an AWG, a power splitter, orsome other demultiplexer device. The optical demultiplexer 222 maysupply multiple optical signals based on receiving one or more opticalsignals, such as WDM signals, or components associated with the one ormore optical signals. Additionally, the optical demultiplexer 222 mayinclude waveguides 224.

The waveguides 224 may include an optical link or some other link totransmit optical signals, output from the optical demultiplexer 222, tothe optical receivers 226. In some implementations, each opticalreceiver 226 may receive optical signals via a single waveguide 224 orvia multiple waveguides 224.

As discussed in greater detail below, the optical receivers 226 may eachinclude one or more photodetectors and related devices to receiverespective input optical signals outputted by the optical demultiplexer222, detect the optical subcarriers associated with the input opticalsignals, convert the optical subcarriers to voltage signals, convert thevoltage signals to digital samples, and process the digital samples toproduce output data corresponding to the one or more data streams, suchas the input client data streams 352-1 to 352-4 associated with inputdata 352 provided to transmitter 212-1, for example. In someimplementations, each of the optical receivers 226 may include a localoscillator, a hybrid mixer, a detector, an ADC, an RX DSP, and/or someother components, as described in greater detail below in relation toFIG. 6.

While FIG. 1 shows the optical network 200 as including a particularquantity and arrangement of components, in some implementations, theoptical network 200 may include additional components, fewer components,different components, or differently arranged components. Also, in someinstances, one of the devices illustrated in FIG. 1 may perform afunction described herein as being performed by another one of thedevices illustrated in FIG. 1.

FIG. 2 is a diagram illustrating an example of components of the opticaltransmitter 212 in greater detail. As shown in FIG. 2, the opticaltransmitter 212 may include a TX DSP 310, two digital-to-analogconverters (DACs) 320-1 and 320-2 (referred to generally as DACs 320 andindividually as DAC 320), a laser 330, modulators 340-1 and 340-2(referred to generally as modulators 340 and individually as modulator340), and a splitter 350.

In some implementations, the TX DSP 310 and the DAC 320 may beimplemented using an application specific integrated circuit (ASIC)and/or may be implemented on a single integrated circuit, such as asingle PIC. In some implementations, the laser 330 and the modulator 340may be implemented on a single integrated circuit, such as a singlephotonic integrated circuit (PIC). In some other implementations, the TXDSP 310, the DAC 320, the laser 330, and/or the modulator 340 may beimplemented on one or more integrated circuits, such as one or morePICs. For example, in some example implementations, components ofmultiple optical transmitters 212 may be implemented on a singleintegrated circuit, such as a single PIC, to form a super-channeltransmitter.

The TX DSP 310 may comprise a digital signal processor. The TX DSP 310may receive input data from multiple data sources, each of whichsupplying a respective one of the plurality of Client Data Streams 352-1through 352-4. In general, “N” number of Client Data Streams 352-1 to352-N can be used. For explanatory purposes, four Client Data Streams352 (N=4) are used in relation to FIG. 2. The TX DSP 310 may determinethe signal to apply to the modulator 340 to generate multiple opticalsubcarriers. Digital subcarriers may comprise electronic signalsgenerated in the TX DSP 310 that correspond to respective opticalsubcarriers.

In some implementations, the TX DSP 310 may receive streams of data(such as one or more of the Client Data Streams 352-1 to 352-4), map thestreams of data into each of the digital subcarriers, independentlyapply spectral shaping to each of the digital subcarriers, and obtain,based on the spectral shaping of each of the digital subcarriers, asequence of values to supply to the DAC 320. In some implementations,the TX DSP 310 may generate the digital subcarriers using time domainfiltering and frequency shifting by multiplication in the time domain.The TX DSP 310 will be further described in relation to FIG. 3.

The DAC 320 may comprise a digital-to-analog converter. The DAC 320 mayreceive the sequence of values and, based on the sequence of values,generate the analog or voltage signals to apply to the modulator 340.

The laser 330 may include a semiconductor laser, such as a distributedfeedback (DFB) laser, or some other type of laser. The laser 330 mayprovide an output optical light beam to the modulator 340.

The modulator 340 may include a Mach-Zehnder modulator (MZM), such as anested MZM, or another type of modulator. The modulator 340 may receivethe optical light beam from the laser 330 and the voltage signals fromthe DAC 320, and may modulate the optical light beam, based on thevoltage signals, to generate a multiple subcarrier output signal(s),such as Output TE Signal 342-1 and Output TM Signal 342-2.

The splitter 350 may include an optical splitter that receives theoptical light beam from the laser 330 and splits the optical light beaminto two branches: one for the first polarization and one for the secondpolarization. In some implementations, the two optical light beams mayhave approximately equal power. The splitter 350 may output one opticallight beam to modulator 340 including first and second modulators 340-1and 340-2, each of which may include a Mach-Zehnder modulator.

The modulator 340-1 may be used to modulate signals of the firstpolarization. The modulator 340-2 may be used to modulate signals of thesecond polarization.

In some implementations, one or more subcarrier may be modulated by themodulator 340 to carry data at different rates (see FIG. 4A illustratingexemplary subcarriers). For example, a first subcarrier SC1 may carrydata at a first rate and a second subcarrier SC2 may carry data at adifferent rate that is higher or lower than the first rate. In addition,one or more subcarrier may be modulated by the modulator 340 to carrydata with different baud rates (see FIG. 4A illustrating exemplarysubcarriers). For example, the first subcarrier SC1 may carry data at orhave an associated a first baud rate and the second subcarrier SC2 maycarry data at or have an associated second baud rate that is higher orlower (different) than the first baud rate.

In some implementations, a first one of a plurality of subcarriers SC1may be modulated in accordance with a first modulation format and asecond one of the plurality of subcarriers SC2 may be modulated inaccordance with a second modulation format different than the firstmodulation format (see FIG. 4A illustrating exemplary subcarriers). Inone implementation, the first modulation format may be one of BPSK,QPSK, and m-QAM, where m is an integer, and the second modulation formatmay be another one of BPSK, QPSK, and m-QAM. In one implementation, thefirst modulation format may be one of BPSK, QPSK, and m-QAM, where m isan integer, and the second modulation format may be an intensitymodulation format.

In some implementations, a plurality of the subcarriers may have avariety of combinations of modulation and data rates configured by thetransmitter and/or by a plurality of transmitters 212. The particularcombination of modulation and data rates of the subcarriers may beconfigured based on the desired distance of transmission, desired errorrate, desired data rate, and/or other requirements and/or restrictionsfor the optical network 200 and/or the end client.

In some implementations, two DACs 320 may be associated with eachpolarization. In these implementations, two DACs 320-1 may supplyvoltage signals to the modulator 340-1, and two DACs 320-2 may supplyvoltage signals to the modulator 340-2. In some implementations, theoutputs of the modulators 340 may be combined back together usingcombiners (e.g., optical multiplexer 216) and polarization multiplexing.

While FIG. 2 shows the optical transmitter 212 as including a particularquantity and arrangement of components, in some implementations, theoptical transmitter 212 may include additional components, fewercomponents, different components, or differently arranged components.The quantity of DACs 320, lasers 330, and/or modulators 340 may beselected to implement an optical transmitter 212 that is capable ofgenerating polarization diverse signals for transmission on an opticalfiber, such as the link 230. In some instances, one of the componentsillustrated in FIG. 2 may perform a function described herein as beingperformed by another one of the components illustrated in FIG. 2.

FIG. 3 shows an example of the digital signal processor (TX DSP) 310 ofthe transmitter 212 in greater detail. In this example, four of theClient Data Streams 352 are shown. The digital signal processor 310 mayinclude FEC encoders 405-1 to 405-4 (referred to generally as FECencoders 405 and individually as FEC encoder 405), input bits components420-1 to 420-4 (referred to generally as input bits components 420 andindividually as input bits component 420), four bits-to-symbolcomponents 430-1 to 430-4 (referred to generally as bits-to-symbolcomponents 430 and individually as bits-to-symbol component 430), fouroverlap-and-save buffers 256 440-1 to 440-4 (referred to generally asoverlap-and-save buffers 440 and individually as overlap-and-save buffer440), four fast Fourier transform functions (FFT) 256 components 450-1to 450-4 (referred to generally as FFT components 450 and individuallyas FFT component 450), four replicator components 460-1 (referred togenerally as replicator components 460 and individually as replicatorcomponent 460), four pulse shape filters 470 (referred to generally aspulse shape filters 470 and individually as pulse shape filter 470), aninverse FFT (IFFT) 2048 component 490, and a take last 1024 component495. Optionally, the TX DSP 310 may further comprise one or morezero-bit-insertion-block circuitry components 475 (referred to generallyas zero-bit-insertion-block circuitry components 475 and individually aszero-bit-insertion-block circuitry component 475), and a memory 2048array 480. Optionally, the TX DSP 310 may further comprise fourzero-bit-insertion-block circuitry components 475 (referred to generallyas zero-bit-insertion-block circuitry components 475 and individually aszero-bit-insertion-block circuitry component 475), and a memory 2048array 480.

For each of the Client Data Streams 352, the digital signal processor(TX DSP) 310 of the transmitter 301 may contain one each of the FECencoders 405, the input bits components 420, the bits-to-symbolcomponents 430, the overlap-and-save buffers 440, the fast Fouriertransform functions (FFT) components 450, the replicator components 460,the pulse shape filters 470, and the zero-bit-insertion-block circuitrycomponents 475.

Each of the FEC encoders 405-1 to 405-4 may receive a particular one ofthe plurality of independent input data streams of bits (illustrated asexemplary Client Data Streams 352-1 to 352-4) from a respective one of aplurality of data sources and perform error correction coding on acorresponding one of the input Client Data Streams 352, such as throughthe addition of parity bits. The FEC encoders 405-1 to 405-4 may bedesigned to generate timing skew between the subcarriers to correct forskew induced by link(s) between the transmitter module 210 and thereceiver module 220 in the optical network 200.

Input bits component 420 may process, for example, 128*X bits at a time,where X is an integer. For dual-polarization Quadrature Phase ShiftKeying (QPSK), X is four. For higher modulation formats, X may be morethan four. For example, for an 8-quadrature amplitude modulation (QAM)format, X may be eight and for a 16 QAM modulation format, X may besixteen. Accordingly, for such 8 QAM modulation, eight FEC encoders 405may be provided, each of which may encode a respective one of eightindependent input data streams (e.g., eight of the Client Data Streams352) for a corresponding one of eight digital subcarriers correspondingto eight optical subcarriers. Likewise, for 16 QAM modulation, sixteenFEC encoders 405 may be provided, each of which may encode a respectiveone of sixteen independent input data streams (e.g., sixteen of theClient Data Streams 352) for a corresponding one of sixteen subcarrierscorresponding to sixteen optical subcarriers.

The bits-to-symbol component 430 may map the bits to symbols on thecomplex plane. For example, the bits-to-symbol components 430 may mapfour bits or other numbers of bits to a symbol in the dual-polarizationQPSK constellation or other modulation format constellation.Accordingly, each of the components or circuits 430 may define ordetermine the modulation format for a corresponding subcarrier. Inaddition, components or circuits 405, 420, and 430 may define ordetermine the baud rate and or data rate for each subcarrier. Therefore,the modulation format, baud rate and data rate may be selected for eachsubcarrier by these circuits. For example, control inputs may beprovided to these circuits so that the desired modulation format, baudrate and data rate may be selected.

The overlap-and-save buffer 440 may buffer 256 symbols, in one example.The overlap-and-save buffer 440 may receive 128 symbols at a time fromthe bits-to-symbol component 430. Thus, the overlap-and-save buffer 440may combine 128 new symbols, from the bits-to-symbol component 430, withthe previous 128 symbols received from the bits-to-symbol component 430.

The FFT component 450 may receive 256 symbols from the overlap-and-savebuffer 440 and convert the symbols to the frequency domain using, forexample, a fast Fourier transform (FFT). The FFT component 450 may form256 frequency bins, for example, as a result of performing the FFT.Components 440 and 450 may carry out the FFT for each subcarrier basedon one sample per symbol (per baud) to thereby convert time domain ordata symbols received by FFT component 550 into frequency domain datafor further spectral shaping (requiring more than one sample/baud orsymbol) by filters 470.

The replicator component 460 may replicate the 256 frequency bins, inthis example, or registers to form 512 frequency bins (e.g., for T/2based filtering of the subcarrier). This replication may increase thesample rate.

The pulse shape filter 470 may apply a pulse shaping filter to the datastored in the 512 frequency bins to thereby provide the digitalsubcarriers with desired spectral shapes and such filtered subcarriersare multiplexed and subject to the inverse FFT 490, as described below.The pulse shape filter 470 may calculate the transitions between thesymbols and the desired spectrum so that the subcarriers can be packedtogether on the channel. The pulse shape filter 470 may also be used tointroduce timing skew between the subcarriers to correct for timing skewinduced by links between nodes in the optical network 200. The pulseshape filters 470 may be raised cosine filters.

The pulse shape filter 470 may have a variable bandwidth. In someimplementations, the bandwidth of the subcarriers may be determined bythe width of the pulse shape filters 470. The pulse shape filters 470may manipulate the digital signals of the subcarriers or digitalsubcarriers to provide such digital subcarriers with an associatedspectral width. In addition, as generally understood, the pulse shapefilter 470 may have an associated “roll-off” factor (α). Consistent withthe present disclosure, however, such “roll-off” may be adjustable orchanged in response to different control inputs to the pulse shapefilter 470. Such variable roll-off results in the pulse shape filter 470having a variable or tunable bandwidth, such that each subcarrier mayhave a different spectral width. In a further example, one of thesubcarriers may have an associated spectral width that is wider than theremaining subcarriers. It is understood that the control inputs may beany appropriate signal, information, or data that is supplied to thepulse shape filter 470, such that the “roll-off” is changed in responseto such signal, information, or data.

The four zero-bit-insertion-block circuitry components 475 may comprisecircuitry to receive the four digital subcarriers from the four pulseshape filters 470 and may output zeros or other bits in bits between ablock of data bits of a first digital subcarrier and a block of databits of a second digital subcarrier to the memory array 480 in order toadjust the frequency spacing or gap between the optical subcarriers, asdiscussed in greater detail below.

The memory array 480 may receive all four of the digital subcarriersfrom the zero-bit-insertion-block circuitry components 475 and the zerosfrom the four zero-bit-insertion-block circuitry components 475. Thememory array 480 may store the outputs of the digital subcarriers andoutput an array of the four digital subcarriers and the zeros from thefour zero-bit-insertion-block circuitry components 475 to the IFFTcomponent 490.

The IFFT component 490 may receive the 2048 element vector and returnthe signal back to the time domain, which may now be at 64 GSample/s.The IFFT component 490 may convert the signal to the time domain using,for example, an inverse fast Fourier transform (IFFT).

The take last 1024 component 495 may select the last 1024 samples, forexample, from IFFT component 490 and output the 1024 samples to the DACs320 of the transmitter 212 (such as at 64 GSample/s, for example).

While FIG. 3 shows the TX DSP 310 as including a particular quantity andarrangement of functional components, in some implementations, the TXDSP 310 may include additional functional components, fewer functionalcomponents, different functional components, or differently arrangedfunctional components.

Returning now to FIG. 2, as previously described, the DACs 320 mayconvert the received samples from the take last component 495 of the TXDSP 310. The modulator 340 may receive the optical light beam from thelaser 330 and the voltage signals from the DAC 320, and may modulate theoptical light beam or CW light from laser 330, based on the voltagesignals, to generate a multiple subcarrier output signal, such as OutputTE Signal 342-1 and Output TM Signal 342-2.

FIGS. 4A-4E illustrate examples of optical subcarriers SC1 to SC4 thatmay be output from the transmitter 212 (similar optical subcarriers maybe output from transmitters in transceivers located at other nodes). Inone example, the optical subcarriers SC1 to SC4 may not spectrallyoverlap with one another and may be, for example, Nyquist subcarriers,which may have a frequency spacing equal to or slightly larger than theindividual subcarrier baud-rate.

As illustrated in FIG. 4A, the optical subcarriers may have one or morespectra or bandwidths, such as, for example, S3 (optical subcarrier SC3)and S4 (optical subcarrier SC4) above frequency f0, which may correspondto a center frequency (f0) of the laser 330 of the transmitter 212. Inaddition, the optical subcarriers may have one or more spectra orbandwidths, such as for S1 (optical subcarrier SC1) and S2 (opticalsubcarrier SC2) below frequency f0.

In one example, the number of digital and optical subcarriers equals anumber of the independent input Client Data Streams 352. For example,Client Data Streams 352-1 to 352-4 from FIG. 3 may be four independentinput data streams corresponding to four optical subcarriers SC1 to SC4in FIG. 4A, such that each of the optical subcarriers carries data orinformation associated with a respective one of the Client Data Streams.In one example, the number of digital and optical subcarriers is morethan the number of the independent input Client Data Streams 352. Forexample, Client Data Streams 352-1 to 352-3 from FIG. 3 may be threeindependent input data streams mapped to four optical subcarriers SC1 toSC4. Two or more of the optical subcarriers, such as the opticalsubcarriers SC3 and SC4, may carry one of the Client Data Streams 352-3.Such an arrangement allows for more data capacity to be dedicated to aparticular Client Data Stream 352.

Frequency bandwidth and roll-off of the subcarriers may be determined byappropriate input to the pulse shape filters 470. The laser frequency(f0) may be centrally positioned within the frequency (f) of thefilters' bandwidth. As illustrated in FIG. 4A, the filter bandwidths foreach of the four pulse shape filters 470 may be the same, for example,and may all have the same roll-off factor (for example, α=0.3),producing four optical subcarriers SC1-SC4 each having the samebandwidth. As illustrated in FIG. 4B, the filter bandwidths for each ofthe four pulse shape filters 470 may be the same, for example, and mayall have the same roll-off factor (for example, α=0.7) differing fromthe roll-off factor of the example of FIG. 4A, producing foursubcarriers SC1-SC4 each having the same bandwidth, but with a largerbandwidth than subcarriers produced by a pulse shape filter 470 having asmaller roll-off factor. Thus, the roll-off factor for each of filters470 may be controlled or adjusted so that corresponding opticalsubcarriers have different spectral widths, as noted above.

FIG. 4C illustrates another example in which the bandwidth of the foursubcarriers is the same. In the example of FIG. 4C, the baud rate ofeach subcarrier is 8.39, and the shaping factor is 1/16 (6.25%), makingthe total width of each subcarrier 8.39*(1+ 1/16)=8.54 GHz. In someimplementations, the roll-off factor can be assigned to be very narrowfor the majority of the subcarriers, while one subcarrier is given awider roll-off factor. This allows for channel spacing to be tighterthan would be possible with conventional shaping and clock recovery.That is, since the majority of subcarriers in this example, have anarrow bandwidth, more subcarriers can be accommodated within a givenamount of spectrum, and, therefore, provide greater data carryingcapacity for a given link. Clock and/or phase recovery based on thewider subcarrier is discussed in greater detail below.

As illustrated in FIGS. 4D and 4E, in some implementations, the filterbandwidths for one or more of the four pulse shape filters 470 may bedifferent that the filter bandwidths of one or more of the other pulseshape filters 470, thereby resulting in one or more of the subcarriershaving a different bandwidth than one or more of the other subcarriers.Additionally or alternately, one or more of the four pulse shape filters470 may have a different roll-off factor (α) than one or more of theother pulse shape filters 470, thereby resulting in one or moresubcarriers having a different bandwidth than the other subcarriers. Forexample, a first, third, and fourth of the pulse shape filters 470-1,470-3, 470-4 may have a first roll-off factor (such as α=0.3) while asecond of the pulse shape filters 470-2 may have a roll-off factordifferent than the other three (such as α=0.7), such that the first,third, and fourth subcarriers SC1, SC3, and SC4, have a first bandwidthand the second subcarrier SC2 has a second bandwidth different than thebandwidths of the other subcarriers. In some implementations, thesubcarrier with the larger bandwidth than the other subcarriers may beused to carry clock-recovery information for a plurality of thesubcarriers, as will be described in relation to FIG. 7.

In the example shown in FIG. 4E, the first subcarrier SC1 is shaped with1.5% roll-off factor, for example; the second subcarrier SC2 is shapedwith 6.25% roll-off factor, for example; and the third subcarrier SC3and the fourth subcarrier SC4 are shaped with 1.5% roll-off factor, forexample. A 1.5% roll-off factor on 8.39 GBaud maps to 8.16 GHz. In thisexample, total spectral width is reduced by 800 MHz in comparison to theexample illustrated in FIG. 4D.

Referring now to FIG. 3 and FIGS. 5A-5D, in some implementations, thesubcarriers may have gaps, or spacing, between the subcarriers createdby the zero-bit-insertion-block circuitry components 475. Thezero-bit-insertion-block circuitry components 475 may insert zeros orother bits within certain locations between the data from a firstsubcarrier and the data associated with one or more second subcarriersinto the memory array 480, which may result in one or more frequencygaps between the optical subcarriers of varying or constant width, asdescribed below.

Varying or controlling the frequency gap will next be described ingreater detail with reference to FIG. 5A, which illustrates memorylocations 0 . . . 2048 included in memory array 480. The memory array480 may include, in one example, an array of such memory locations,whereby selected locations store complex numbers output from filters470, as well as, in one example, 0 bits. Such complex numbers constitutefiltered frequency domain data associated with each subcarrier. Thesenumbers may then be output to IFFT component 490, which, in turnsupplies a time domain signal, and, based on such time domain signal,analog signals are generated for driving modulators 340 to output theoptical subcarriers. Thus, by selecting memory locations that store 0bits and other locations that store the frequency domain data, theinputs to IFFT component 490 may be set to result in particularfrequency assignments and spacings of the optical subcarriers.

In the example shown in FIG. 5A, filters 470-1 to 470-4 output frequencydomain data to location groupings L1 to L4, respectively in memory 480.Each of memory location groupings L-1 to L-4 may store such frequencydomain data as complex numbers, and each such complex number may bestored in a respective location in each grouping. In one example, eachof memory location groupings L-1 to L-4 may have 256 locations, each ofwhich storing a respective one of 256 complex numbers. In addition,zero-bit-insertion-block circuitry components 475 may provide zero bitsor other numbers to location groupings Z1 to Z4, respectively, in memory480. Memory location groupings Z1 to Z5 including those memory remaininglocations in memory 480 other than the locations included in locationsL1 to L4. When the resulting combination of numbers in locationgroupings L1 to L4 and the zero bits stored in locations Z1 to Z5 ofmemory 480 are output to the IFFT component 490, the IFFT component 490outputs time domain signals, in digital form, that result in opticalsubcarriers SC1 to SC4 having frequencies f1 to f4, respectively, asshown in FIG. 5A, and associated frequency gaps G1-1 to G1-3, as furthershown in FIG. 5A.

As further shown in FIG. 5A, the frequency domain data stored inlocations L-1 is associated with and corresponds to data carried bysubcarrier SC3; the frequency domain data stored in locations L-2 isassociated with and corresponds to data carried by subcarrier SC4; thefrequency domain data stored in locations L-3 is associated with andcorresponds to data carried by subcarrier SC1; and the frequency domaindata stored in locations L-1 is associated with and corresponds to datacarried by subcarrier SC4.

Similarly, as shown in FIG. 5B, the filters 570-1 to 570-4 outputfrequency domain data to location groupings L2-1 to L2-4, respectivelyin the memory 480. In addition, zero-bit-insertion-block circuitrycomponents 475 may provide zero bits to location groupings Z2-1 to Z2-4,respectively, in the memory 480. When the resulting combination ofnumbers stored in location groupings L1 to L4 and the zero bits storedin locations Z1 to Z5 of memory 480 are output to the IFFT component490, the IFFT component 490 outputs time domain signals, in digitalform, that result in optical subcarriers SC1 to SC4 having frequenciesf1′ to f4′, respectively in FIG. 5B, and associated frequency gaps G2-1to G2-3, as further shown in FIG. 5B. Frequencies f1′ to f4′ may differfrom frequencies f1 to f4, and frequency gaps G2-1 to G2-3 may differfrom frequency gaps G1 to G3. Thus, based on the locations frequencydomain data and the zero bit data the gaps and frequencies of thesubcarriers can be controlled or adjusted, such that different locationsin which the frequency domain and zero bit data are stored can result indifferent subcarrier frequencies and gaps.

FIGS. 5C and 5D illustrate further examples of subcarriers havingvariable spacing between the subcarriers and varying combinations ofspacing between groups of subcarriers. For example, in FIG. 5C, a firstgroup of subcarriers SC1-SC4 in a first carrier C1 (such as from a firsttransmitter 212) are routed together, with a gap G2 between the firstcarrier C1 and a second carrier C2 (such as from a second transmitter212) having a second group of subcarriers SC1-SC4. Additionally, FIG. 5Cillustrates another pattern of carriers Cn−1, Cn, Cn+1, in which a pairof subcarriers SC2, SC4 from a first carrier Cn−1 are routed with a pairof subcarriers SC3, SC1 from a second subcarrier Cn; while a pair ofsubcarriers SC2, SC4 from the second carrier Cn are routed with a pairof subcarriers SC3, SC1 from a third subcarrier Cn+1; with a gap G2between the first subcarrier SC1 in Cn−1 and the second subcarrier SC2in Cn−1, and also with a gap G2 between the first subcarrier SC1 in Cnand the second subcarrier SC2 in Cn, and so on. The pattern of groupingof and spacing between subcarriers may repeat for multiple carriers Cn,or may vary. Each of carriers Cn may be supplied from a correspondingone of transmitters 370.

In another example, FIG. 5D illustrates a variety of combinations ofrouting of subcarriers with and without gaps between exemplary carriersC1, C2, C3, and C4 and/or subcarriers within the carriers Cn. In thisexample, an Intra-Carrier Gap (G) may be allocated between 0, 1, 2 or Nof the subcarriers. The Intra-Carrier Gap (G) may be the total gapbudgeted for the channel. The size of the gaps G1, G2, . . . Gn, betweenthe subcarriers may range from zero GHz to a maximum of the totalIntra-Carrier Gap G. In the example illustrated in FIG. 5D, G1=6.25 GHz.The frequency width of the subcarriers SC1, SC2, SC3, SC4 in a carrierCn may vary. In the example of FIG. 5D, a combination of gaps G1 is usedwith the illustrated carriers C1-C4. For example, in carrier C1, a gapG1 is shown between each of the subcarriers SC1-SC4, and between thecarrier C1 and the carrier C2. Further in this example, in carriers C2and C3, no gap is shown between the respective subcarriers SC3 and SC1or SC2 and SC4, while a gap G1 is shown between the respectivesubcarriers SC1 and SC2 and between the carrier C2 and the carrier C3.In the example, carrier 4 does not have gaps between the subcarriers orbetween carrier 4 and carrier 3, but does have a gap between carrier 4and any additional carriers.

In one implementation, the subcarriers may not occupy the centerfrequency ω_c (that is, the laser wavelength). The frequency width of acarrier (Cn) may equal the sum of the frequency width of the subcarriersplus the sum of the frequency width of the gaps Gn (that is, the totalIntra-Carrier Gap G). In another implementation, up to a maximum of halfof the total Intra-Carrier gaps G may be allocated on either side of thecenter frequency ω_c, that is, the laser frequency. It will beunderstood that these combinations of spacing are exemplary, and thatany combination of spacing between subcarriers and/or carriers may beused.

The variable spacing of the subcarriers may be based at least in part onthe routing and/or destination of the subcarriers. For example, thetypes of filters in the OADMs 229 and/or their widths and/or the numberof filters in the route through the optical network 200 that thesubcarrier will take, as well as the number and locations of receivers226, and the capacity of such receivers 226, may determine the number ofsubcarriers, the width of the subcarriers, the frequencies of thesubcarriers, and/or the spacing between the subcarriers that aretransmitted in a particular optical network 200. The spacing of thesubcarriers may be based at least in part on one or more data rate ofone or more of the subcarriers.

An example of subcarrier frequency selection based on filter bandwidthwill next be described with reference to FIG. 5E. As noted above,optical signals including subcarriers may be output from transmitters212 onto optical fiber link 230. The optical signals may be transmittedthrough OADMs 229-1 and 229-2 coupled along fiber link 230. Each ofOADMs 229-1 and 229-2 may include wavelength selective switches, each ofwhich may further including one or more optical filters. One of theseoptical filters provided in OADM 229-1, for example, may have abandwidth or transmission characteristic 529-1 defined by edgefrequencies f2 and f4, and at least one of the optical filters in OADM229-2 may have a bandwidth or transmission characteristic 529-2 definedby frequencies f5 and f6. In order to transmit an optical subcarrier,such as optical subcarrier SC1 through filters in both OADM 229-1 and229-2, the frequency of the optical subcarrier is preferably selected tobe within a high transmission frequency range R that is common to bothfilter bandwidths 529-1 and 529-2. As further shown in FIG. 5E, range Ris defined by edge frequency F4 of bandwidth 529-1 and edge frequency f5of bandwidth 529-2. Accordingly, the frequency f1 of optical subcarrierSC1 is controlled or selected by controlling the subcarrier gap in amanner similar to that described above so that optical subcarrier SC1falls within the high transmission frequency range R that is common toor overlaps between filter bandwidths 529-1 and 529-2.

Returning now to FIG. 1, in one example, optical subcarriers that areoutput from the transmitter 212 may be supplied to the multiplexer 216and sent via the link 230 to one or more receiver module, such asreceiver module 220, which may select data carried by one of suchoptical subcarriers, as described in greater detail below with referenceto FIGS. 6 and 7.

At the receiver module 220, the optical subcarriers may be supplied toone or more of the receivers 226. FIG. 6 illustrates an exemplary one ofthe optical receivers 226 of the receiver module 220. The opticalreceiver 226 may include a polarization beam splitter 605 (having afirst output 606-1 and a second output 606-2), a local oscillator laser610, two ninety-degree optical hybrids or mixers 620-1 and 620-2(referred to generally as hybrid mixers 620 and individually as hybridmixer 620), two detectors 630-1 and 630-2 (referred to generally asdetectors 630 and individually as detector 630, each including either asingle photodiode or balanced photodiode), two analog-to-digitalconverters (ADCs) 640-1 and 640-2 (referred to generally as ADCs 640 andindividually as ADC 640), and a receiver digital signal processor (RXDSP) 650.

The polarization beam splitter (PBS) 605 may include a polarizationsplitter that splits an input optical signal 607, having opticalsubcarriers, as noted above, into two orthogonal polarizations, such asthe first polarization and the second polarization. The hybrid mixers620 may combine the polarization signals with light from the localoscillator laser 610. For example, the hybrid mixer 620-1 may combine afirst polarization signal (e.g., the component of the incoming opticalsignal having a first or TE polarization output from the first output606-1) with the optical signal from the local oscillator 610, and thehybrid mixer 620-2 may combine a second polarization signal (e.g., thecomponent of the incoming optical signal having a second or TMpolarization output from the second output 606-2) with the opticalsignal from the local oscillator 610. In one example, a polarizationrotator may be provided at the second output 606-2 to rotate the secondpolarization to be the first polarization.

The detectors 630 may detect mixing products output from the opticalhybrid mixers 620, to form corresponding voltage signals. The ADCs 640may convert the voltage signals to digital samples. For example, twodetectors 630-1 (or photodiodes) may detect the first polarizationsignals to form the corresponding voltage signals, and a correspondingtwo ADCs 640-1 may convert the voltage signals to digital samples forthe first polarization signals after amplification, gain control and ACcoupling. Similarly, two detectors 630-2 may detect the secondpolarization signals to form the corresponding voltage signals, and acorresponding two ADCs 640-2 may convert the voltage signals to digitalsamples for the second polarization signals after amplification, gaincontrol, and AC coupling.

The RX DSP 650 may process the digital samples for the first and secondpolarization signals to generate resultant data, which may be outputtedas output data 652, such as Client Data Streams 352.

While FIG. 6 shows the optical receiver 226 as including a particularquantity and arrangement of components, in some implementations, theoptical receiver 226 may include additional components, fewercomponents, different components, or differently arranged components.The quantity of detectors 630 and/or ADCs 640 may be selected toimplement an optical receiver 226 that is capable of receiving apolarization diverse signal. In some instances, one of the componentsillustrated in FIG. 6 may perform a function described herein as beingperformed by another one of the components illustrated in FIG. 6.

Consistent with the present disclosure, in order to select one or moreoptical subcarriers at a remote node, the local oscillator laser 610 maybe tuned to output light having a wavelength relatively close to theselected optical subcarrier(s) wavelength(s) to thereby cause a beatingbetween the local oscillator light and the selected opticalsubcarrier(s). Such beating will either not occur or will besignificantly attenuated for the other non-selected optical subcarriersso that data from the Client Data Stream(s) 352 carried by the selectedoptical subcarrier is detected and processed by the Rx DSP 650.

In the example shown in FIG. 6, appropriate tuning of the wavelength ofthe local oscillator laser 610 enables selection of one of the opticalsubcarriers, e.g., optical subcarrier SC1, carrying signals or dataindicative of Client Data Stream 352-1. Accordingly, optical subcarriersmay be effectively routed through the optical network 200 to a desiredreceiver 226 in a particular node of the optical network 200.

Accordingly, at each receiver 226, the local oscillator laser 610 may betuned to have a wavelength close to that of one of the opticalsubcarriers carrying signals and data indicative of the desired clientdata from the Client Data Stream 352 to be output from the Rx DSP 650.Such tuning may be achieved by adjusting a temperature or currentflowing through local oscillator laser 610, which may include asemiconductor laser, such as a distributed feedback (DFB) laser ordistributed Bragg reflector (DBR) laser (not shown). Thus, differentoptical components in each receiver are not required to select opticalsignals carrying a desired data stream. Rather, as noted above, the sameor substantially the same circuitry may be provided in the receivermodule 220 of each node, in the optical network 200, and signal or dataselection may be achieved by tuning the local oscillator laser 610 tothe desired beating wavelength.

As further shown in FIG. 6, the Rx DSP 650 may have output data 652,such that based on such output, the temperature of, or the currentsupplied to, local oscillator laser 610 may be controlled. In the caseof temperature control, a thin film heater may be provided adjacentlocal oscillator laser 610, and an appropriate current may be suppliedto such heater, based on output 652, to heat laser 610 to the desiredtemperature. Control circuitry in the Rx DSP 650 may generate output orcontrol the output signal 652. Additionally or alternatively, suchcircuitry may be provided outside the Rx DSP 650.

FIG. 7 illustrates exemplary components of an example of the receiverdigital signal processor (Rx DSP) 650 shown in FIG. 6. The RX DSP 650may include an overlap and save buffer 805, a FFT component 810, ade-mux component 815, four fixed filters 820-1 to 820-4 (referred togenerally as fixed filters 820 and individually as fixed filter 820),four polarization mode dispersion (PMD) components 825-1 to 825-4(referred to generally as PMD components 825 and individually as PMDcomponent 825), four IFFT components 830-1 to 830-4 (referred togenerally as IFFT components 830 and individually as IFFT component830), four take last 128 components 835-1 to 835-4 (referred togenerally as take last 128 components 835 and individually as take last128 component 835), four carrier recovery components 840-1 to 840-4(referred to generally as carrier recovery components 840 andindividually as carrier recovery component 840), four symbols to bitscomponents 845-1 to 845-4 (referred to generally as symbols to bitscomponents 845 and individually as symbols to bits component 845), fouroutput bits components 850-1 to 850-4 (referred to generally as outputbits components 850 and individually as output bits component 850), andfour FEC decoders 860-1 to 860-4 (referred to generally as FEC decoders860 and individually as FEC decoder 860). In one implementation, thereceiver digital signal processor 650 may optionally include a clockrecovery circuit 817.

In greater detail, the overlap and save buffer 805 may receive samplesfrom the ADCs 640-1 and 640-2. In one implementation, the ADC 640 mayoperate to output samples at 64 G Sample/s. The overlap and save buffer805 may receive 1024 samples and combine the current 1024 samples withthe previous 1024 samples, received from the ADC 640, to form a vectorof 2048 elements. The FFT component 810 may receive the 2048 vectorelements, for example, from the overlap and save buffer 805 and convertthe vector elements to the frequency domain using, for example, a fastFourier transform (FFT). The FFT component 810 may convert the 2048vector elements to 2048 frequency bins as a result of performing theFFT.

The de-mux component 815 may receive the 2048 frequency bins or outputsfrom FFT component 810. The de-mux component 815 may demultiplex the2048 frequency bins to element vectors for each of the subcarriers, forexample, 512 vectors, which may have, in one example an associated baudrate of 8 Gbaud.

In some implementations, clock and/or phase recovery circuitry 817 maybe connected or coupled between the de-mux component 815 and the filter820. In cases where one of the subcarriers (such as SC2 in FIGS. 4H-4I)has a wider bandwidth, due to a corresponding roll-off in the associatedtransmitter filter 470 discussed above, than the other subcarriers, thewider subcarrier SC2 may be selected from the output of the de-muxcomponent 815 for clock recovery and the recovered or detected clock orphase related signal may be provided to the ADCs 640 in the receiver 226(see FIG. 6). The clock may be used to set and/or adjust the timing ofsampling of the ADCs 640 for the plurality of the subcarriers.

The clock may be recovered using information from all subcarriers, orfrom fewer than all the subcarriers, or just from one subcarrier. Insome implementations, clock recovery with the clock recovery circuit 817in the RX DSP 650 of the receiver 226 is based on the subcarrier withthe widest bandwidth and associated filter 470 having a correspondingroll-off (such as subcarrier SC2 in FIGS. 4D and 4E). The subcarrierwith the widest bandwidth may be used to recover the clock signal andsuch clock signal may be used for the other ADCs 640.

In one example, where the data associated with more than one ofsubcarriers SC1-SC4, such as subcarriers SC2 and SC3, is to be outputfrom the receiver 226, the clock recovered from the widest subcarrierSC2 may be used as the clock for the other subcarriers SC1, SC3, andSC4. As noted above, by reducing the frequency bandwidth of the othersubcarriers SC1, SC3, and SC4, more subcarriers fit in a given spectrumor bandwidth to thereby increase overall capacity (as shown in FIGS. 4Hand 4I). In one example, where each node outputs the data of only onesubcarrier SC1, clock recovery may be performed based on thecorresponding subcarrier SC1 to be detected at that node 202.

Fixed filters 820 may apply a filtering operation for, for example,dispersion compensation or other relatively slow varying impairment ofthe transmitted optical signals and subcarriers. The fixed filters 820may also compensate for skew across subcarriers introduced in the link230, or skew introduced intentionally in optical transmitter 212.

The PMD component 825 may apply polarization mode dispersion (PMD)equalization to compensate for PMD and polarization rotations. The PMDcomponent 825 may also receive and operate based upon feedback signalsfrom the take last 128 component 835 and/or the carrier recoverycomponent 840.

The IFFT component 830 may covert the 512 element vector, in thisexample, (after processing by the fixed filter component 820 and the PMDcomponent 825) back to the time domain as 512 samples. The IFFTcomponent 830 may convert the 512 element vector to the time domainusing, for example, an inverse fast Fourier transform (IFFT). The takelast 128 component 835 may select the last 128 samples from the IFFTcomponent 830 and output the 128 samples to the carrier recoverycomponent 840.

The carrier recovery component 840 may apply carrier recovery tocompensate for transmitter and receiver laser linewidths. In someimplementations, the carrier recovery component 840 may perform carrierrecovery to compensate for frequency and/or phase differences betweenthe transmit signal and the signal from the local oscillator 610. Aftercarrier recovery, the data may be represented as symbols in the QPSKconstellation or other modulation formats. In some implementations, theoutput of the take last 128 component 835 and/or the carrier recoverycomponent 840 could be used to update the PMD component 825.

The symbols to bits component 845 may receive the symbols output fromthe carrier recovery component 840 and map the symbols back to bits. Forexample, the symbol to bits component 845 may map one symbol, in theQPSK constellation, to X bits, where X is an integer. Fordual-polarization QPSK, X is four. In some implementations, the bitscould be decoded for error correction using, for example, FEC. Theoutput bits component 850 may output 128*X bits at a time, for example.For dual-polarization QPSK, the output bits component 850 may output 512bits at a time, for example.

The FEC decoder 860 may process the output of the output bits component850 to remove errors using forward error correction. As further shown inFIG. 7, a switch, blocking, or terminating circuit 865 may be providedto terminate one or more client data streams 352 that are not intendedfor output from receiver 226.

While FIG. 7 shows the RX DSP 650 as including a particular quantity andarrangement of functional components, in some implementations, the RXDSP 650 may include additional functional components, fewer functionalcomponents, different functional components, or differently arrangedfunctional components.

In some implementations, the subcarriers may have variable and flexiblecapacity per subcarrier, but fixed subcarrier width such as a fixed baudrate per subcarrier. Such parameters may be selected or set in a mannersimilar to that described above. An exemplary optical network 200 havingsubcarriers with flexible capacity and fixed width may includeindependent clock and carrier recovery for each subcarrier or the clockrecovery for one subcarrier may be used for other subcarriers, asdescribed previously. FIGS. 8A-8G illustrates some such examples in use.For explanatory purposes, FIGS. 8A-8G illustrate use case examples witha constant baud rate of 16 GHz per subcarrier. The subcarriers for eachexample may be transmitted from one transmitter 212 or from acombination of two or more transmitters 212.

In the example of FIG. 8A, the subcarriers SC1-SC6 are modulated at128QAM to be transferred 100 km, with a constant baud rate of 16 GHz persubcarrier, and 175G bit rate per subcarrier. In the example of FIG. 8B,the subcarriers SC1-SC6 are modulated at 64QAM to be transferred 500 km,with a constant baud rate of 16 GHz per subcarrier, and 150G bit rateper subcarrier. In the example of FIG. 8C, the subcarriers SC1-SC6 aremodulated at 32QAM to be transferred 1000 km, with a constant baud rateof 16 GHz per subcarrier, and 125G bit rate per subcarrier. In theexample of FIG. 8D, the subcarriers SC1-SC6 are modulated at 16QAM to betransferred 2000 km, with a constant baud rate of 16 GHz per subcarrier,and 100G bit rate per subcarrier.

In the example of FIG. 8E, the subcarriers SC1-SC4 are modulated at128QAM to be transferred a variety of distances, with a constant baudrate of 16 GHz per subcarrier, with a variety of bit rates persubcarrier, and illustrating frequency spacing between subcarrier SC1and subcarrier SC2, as well as between subcarrier SC3 and subcarrierSC4, such as described in relation to FIGS. 5A-5D. In the example ofFIG. 8F, the subcarriers SC1-SC5 are modulated at 64QAM to betransferred a variety of distances, with a constant baud rate of 16 GHzper subcarrier, with a variety of bit rates per subcarrier, andillustrating frequency spacing between subcarrier SC3 and subcarrierSC4, such as described in relation to FIGS. 5A-5D. In the example ofFIG. 8G, the subcarriers SC1-SC6 are modulated at 16QAM to betransferred a variety of distances, with a constant baud rate of 16 GHzper subcarrier, and with a variety of bit rates per subcarrier.

Though the examples of FIGS. 8A-8G show particular exemplaryconfigurations of subcarriers having variable and flexible capacity persubcarrier, and having fixed subcarrier width such as a fixed baud rateper subcarrier, the subcarriers may have any combination of data rates,modulations, spacing, and/or number of subcarriers, and/or otherconfiguration factors. Additionally, two or more of the subcarriers maybe provided from one transmitter 212 or from two or more transmitters212 and from one transmitter module 210 or from two or more transmittermodules 210. The particular combination and/or configuration ofsubcarriers used may be based on requirements for transmission distance,data rates, error rates, and/or filter configurations, for example.

In some implementations, the subcarriers may have flexible width, butthe capacity of each subcarrier may be fixed. Such parameters may be setin a manner similar to that described above. To maintain a constant bitrate, the width of the subcarriers may vary as discussed above, but thedata rate may be controlled to be the same as further noted above. Anexemplary optical network 200 having subcarriers with flexible width andfixed capacity may include independent clock and carrier recovery foreach subcarrier (though the subcarriers may optionally be tiedtogether). The position of the subcarriers may be arbitrary within theanalog bandwidth, as described above. FIGS. 9A-9D illustrates some suchexamples in use. For explanatory purposes, the capacity of eachsubcarrier in FIGS. 9A-9D may be fixed at 100G per subcarrier.

In the example of FIG. 9A, the subcarriers SC1-SC6 are modulated atgreater than 64QAM to be transferred a variety of distances with aconstant bit rate of 100G and illustrating frequency spacing betweensubcarrier SC2 and subcarrier SC3, as well as between subcarrier SC5 andsubcarrier SC6, such as described in relation to FIGS. 5A-5D. In theexample of FIG. 9B, the subcarriers SC1-SC7 are modulated atapproximately 64QAM to be transferred a variety of distances with aconstant bit rate of 100G and illustrating frequency spacing betweensubcarrier SC5 and subcarrier SC6, such as described in relation toFIGS. 5A-5D.

In the example of FIG. 9C, the subcarriers SC1-SC4 are modulated at32QAM to be transferred a variety of distances with a constant bit rateof 100G and illustrating frequency spacing between subcarrier SC1 andsubcarrier SC2 and subcarrier SC3 and subcarrier SC4, such as describedin relation to FIGS. 5A-5D. In the example of FIG. 9D, the subcarriersSC1-SC7 are modulated at 16QAM to be transferred a variety of distanceswith a constant bit rate of 100G.

Though the examples of FIGS. 9A-9D show particular exemplaryconfigurations of subcarriers having flexible width, but the capacity ofeach subcarrier may be fixed, the subcarriers may have any combinationof widths, modulations, spacing, and/or number of subcarriers and/orother configuration factors. Additionally, two or more of thesubcarriers may be provided from one transmitter 212 or from two or moretransmitters 212 and from one transmitter module 210 or from two or moretransmitter modules 210. The particular combination and/or configurationof subcarriers used may be based on requirements for transmissiondistance, data rates, error rates, and/or filter configurations, forexample.

FIG. 1, discussed above, shows an example of an optical network 200having a point-to-point configuration. It is understood, that othernetwork or system configurations or architectures are contemplatedherein. Examples of such architectures are discussed in greater detailbelow. The optical subcarriers may be transmitted and received in avariety of types of optical networks 200. For example, FIG. 10illustrates an exemplary optical network 200 a having a mesh networkconfiguration consistent with a further aspect of the presentdisclosure. The mesh network configuration may include three or morenodes 202-1 to 202-n (referred to as nodes 202 and individually as node202), each node 202 having at least one of the transmitter module 210and the receiver module 220 such as previously described, but not shownin FIG. 10 for purposes of clarity. The nodes 202 may be interconnectedby one or more of the links 230, thereby forming a mesh configuration.For purposes of clarity, not all links 230 are numbered in FIG. 10.

In the optical network 200 a, one or more optical subcarriers, such asoptical subcarriers SC1-SC4, may be routed to different nodes 202 in theoptical network 200 a. For example, a first optical subcarrier SC1 maybe routed from node 202-1 to node 202-2, while a second opticalsubcarrier SC2 may be routed from node 202-1 to node 202-8. In theoptical network 200 a, one or more optical subcarriers, such as opticalsubcarriers SC1-SC4, may be directed to the same node 202. For example,four optical subcarriers SC1-SC4 may be routed from node 202-1 to node202-4.

In the optical network 200 a, a particular node 202 may detect multipleoptical subcarriers or may be configured to detect only particularoptical subcarriers or one optical subcarrier. For example, node 202-4may receive four optical subcarriers SC1-SC4 and detect two opticalsubcarriers SC1 and SC4.

In some implementations, a particular node 202 may receive a pluralityof optical subcarriers, and transfer on to another node 202 differentdata in one or more of the optical subcarriers. For example, node 202-2may receive optical subcarriers SC1 and SC3, but may place new data intooptical subcarrier SC1-1 and transmit the optical subcarriers SC1-1 andSC3 to node 202-3.

FIG. 11A illustrates an exemplary optical network 200 b having a ringnetwork configuration consistent with a further aspect of the presentdisclosure. The ring network configuration may include three or more ofthe nodes 202 interconnected by two or more of the links 230 to form aring. The links 230 may be bi-directional between the nodes 202. In theexample illustrated in FIG. 11A, a simple ring configuration is shownhaving five nodes 202, though it will be understood that a differentnumber of nodes 202 in a ring configuration may be included. Such aconfiguration reduces the number of optics assemblies (transmitter andreceiver) from two sets per node 202 to one set per node 202. However,one of the nodes 202 in the optical network 200 b (here, illustrated asNode 1) may still utilizing two sets of optics assemblies, such as twosets of transmitters 212 and receivers 226.

One or more optical subcarriers may be transmitted within the opticalnetwork 200 b. In this example of the optical network 200 b in the ringnetwork configuration, subcarriers SC1-SC5 may be transmitted within theoptical network 200 b. For example, a first optical subcarrier SC1 maybe transmitted bi-directionally on bi-directional fibers between Node 1and Node 5. Similarly, a second optical subcarrier SC2 may betransmitted bi-directionally on bi-directional fibers between Node 5 andNode 4; a third optical subcarrier SC3 may be transmittedbi-directionally on bi-directional fibers between Node 4 and Node 3; afourth optical subcarrier SC4 may be transmitted bi-directionally onbi-directional fibers between Node 3 and Node 2; and a fifth opticalsubcarrier SC5 may be transmitted bi-directionally on bi-directionalfibers between Node 2 and Node 1.

FIG. 11B illustrates exemplary components of Node 5, comprising atransmitter 212, a receiver 226, a laser (LO), a de-mux component 902,and a combiner component 904. The de-mux component 902 may be configuredto split the optical subcarriers from the transmitter to direct theoptical subcarriers to particular other nodes. In this example, thede-mux component 902 may split the optical subcarriers SC1 and SC2 fromthe transmitter 212 to direct optical subcarrier SC1 to Node 1 andoptical subcarrier SC2 to Node 4. The combiner component 904 may beconfigured to combine the optical subcarriers entering Node 5 to thereceiver 226. In this example, the de-mux component 902 may combine theoptical subcarriers SC1 and SC2.

FIG. 12A illustrates an exemplary optical network 200 c having a hubconfiguration consistent with a further aspect of the presentdisclosure. The optical network 200 c may comprise a hub 920, a powersplitter 922, and two or more leaf nodes.

The hub 920 may have a transmitter 212 and a receiver 226. The hub 920may output a plurality of subcarriers, such as, for example, SC1-SC4, tothe power splitter 922. The power splitter 922 may supply a power splitportion of the plurality of optical subcarriers to one or more leafnode, such as, for example, Leaf 1-4. Each Leaf Node may comprise areceiver 226 that may receive all the optical subcarriers SC1-SC4 andthat may output less than all of the data from the client data streamsof all of the optical subcarriers. For example, Leaf 1 may detect all ofthe optical subcarriers SC1-SC4, but may output the data from the datastream from one of the optical subcarriers SC1. As described aboveregarding FIG. 7, the switch, blocking, or terminating circuit 865 inthe receiver 226, may select one of the optical subcarriers (or lessthan all of the optical subcarriers) and may output data from one of theclient data streams 352 (or less than all of the data streams).

FIG. 12B illustrates an exemplary optical network 200 d having a hubconfiguration consistent with a further aspect of the presentdisclosure. The optical network 200 c may comprise a hub 920, wavelengthselective switch (WSS) or de-mux component 930, and two or more leafnodes (Leaf 1-Leaf 4). The WSS or de-mux component 930 may output lessthan all of the optical subcarriers received from the hub 920 to aparticular one of the leaf nodes. For example, the hub 920 may output aplurality of optical subcarriers, for example, SC1-SC4 to the WSS orde-mux component 930, and the WSS or de-mux component 930 may outputless than all of the plurality of optical subcarriers to the leaf nodes,such as, for example, outputting optical subcarrier SC1 to Leaf 1, whilenot outputting optical subcarriers SC2-SC4 to Leaf 1. Additionally, theleaf nodes may each, on a separate fiber, transmit a correspondingoptical subcarrier back to the WSS or de-mux component 930, which maydetect all of the optical subcarriers SC-SC4 and output them to the hub920.

FIG. 13 illustrates an exemplary optical network 200 e having a ring andhub network configuration consistent with a further aspect of thepresent disclosure. The optical network 200 d may include two or morenodes 202 interconnected with one another, such as exemplary nodes 202-1to 202-4, and further interconnected with at least one hub 206. The hub206 may comprise a transmitter 212 and a receiver 226 and may send andreceive a plurality of optical subcarriers, such as, for example,SC1-SC4. Each of the nodes 202-1 to 202-4 on the ring may detect andoutput the data associated with a particular optical subcarrier of theplurality of subcarriers. A particular node may also transmit new dataon the particular subcarrier. The optical network 200 e may havebi-directional fibers between nodes 202 for bi-directional transmission.In some implementations, a plurality of optical subcarriers may all betransmitted to all of the nodes 202, and each particular node 202 mayextract and add a particular subcarrier from the plurality ofsubcarriers. For example, subcarriers SC1-SC4 may be sent to node 202-1,which may extract data from optical subcarrier SC1 and add data tooptical subcarrier SC1 and transmit all of the optical subcarriersSC1-SC4 on to node 202-2. Node 202-2 may receive all of the opticalsubcarriers SC1-SC4, and may extract data from optical subcarrier SC2and add data to subcarrier SC2 and transmit all of the opticalsubcarriers SC1-SC4 on to node 202-3, and so on.

The below table illustrates a list of exemplary spectral efficiencies(that is, bits per unit spectrum) consistent with the presentdisclosure:

Spectral Efficiency Format RSNR RSNR-PS # Bins Fbaud Interpolation MaxCap 11.64  64QAM: 9; 32QAM: 2 17.8 17 88 11.3 11:32 800 10.67  64QAM: 1;32QAM: 2 16.6 15.4 96 12.3 3:8 800 9.85 32QAM: 12; 16QAM: 1  15.3 14.3104 13.3 13:32 700 9.14  32QAM: 4; 16QAM: 3 14.4 13.3 112 14.3  7:16 6008.53  32QAM: 4; 16QAM: 11 13.5 12.5 120 15.4 15:32 600 8 16QAM 12.5 11.8128 16.4 1:2 600 7.11 16QAM: 5; 8QAM: 4  11.4 10.6 144 18.4  9:16 5006.4 16QAM: 1; 8QAM: 4  10.2 9.7 160 20.5 5:8 400 5.82 8QAM: 10; QPSK: 1 9.2 8.8 176 22.5 11:16 400 5.33 8QAM: 2; QPSK: 1 8.6 8.1 192 24.6 3:4400 4.92 8QAM: 6; QPSK: 7 7.9 7.5 208 26.6 13:16 300 4.57 8QAM: 2; QPSK:5 7.3 7.0 224 28.7 7:8 300 4 QPSK 6 6 256 32.8 1:1 300

In accordance with one aspect of the present disclosure, optical powerof one or more optical subcarrier may be controlled individually. Assuch, the optical power of one or more optical subcarrier may differfrom the optical power of one or more other optical subcarrier. Forexample, the digital signal processor 310 of the transmitter 212 mayinclude power adjusting circuitry such as, but not limited to, aplurality of digital multipliers 478 corresponding to the plurality ofindependent data streams 352-1 to 352-4, the plurality of digitalmultipliers 478 configured to control power gain of the digitalsubcarriers, which results in control of the optical power of theoptical subcarriers. The power adjusting circuitry, such as theplurality of digital multipliers 478 may be configurable so as tocontrol and/or change power gains for specific ones of the plurality ofdigital subcarriers. One or more gain control signals 479 may be used toconfigure the power adjusting circuitry, such as the plurality ofdigital multipliers 478. In one implementation, the one or more gaincontrol signals 479 may be generated by one or more processors 481.

In one aspect of the present disclosure, the plurality of digitalmultipliers 478 may be located within the digital signal processor 310between the FFT component 450 and the IFFT component 490.

FIG. 14 illustrates a diagram of components of an exemplary digitalsignal processor 310 a of an exemplary transmitter 212 which may be usedto configure the power gain to digital subcarriers SC1-SC4. In thefollowing figures, four digital subcarriers are shown for explanatorypurposes, but it will be understood that any number of digitalsubcarriers SCN may be used. One or more digital multiplier 478, forexample, digital multipliers 478-1 to 478-4 corresponding to the digitalsubcarriers SC1-SC4, may be used to control the level of power of thedigital subcarriers SC1-SC4. The digital subcarriers SC1-SC4 may then beprocessed through a subcarrier filter 470 a, which may be a pulse shapefilter, and a multiplexer 482.

FIG. 15 illustrates a diagram of another exemplary digital signalprocessor 310 b of an exemplary transmitter 212 which may be used toconfigure the power gain to digital subcarriers SC1-SC4. One or moredigital multiplier 478, for example, digital multipliers 478-1 to 478-4corresponding to the digital subcarriers SC1-SC4, may be used to controlthe level of power of the digital subcarriers SC1-SC4. The digitalsubcarriers SC1-SC4 may then be processed through the pulse shapefilters 470 and the multiplexer 482, before proceeding to the IFFTcomponent 490 and the take last component 495, as previously describedin relation to FIG. 3.

The pulse shape filters 470 may be configured to shape the frequencybandwidths of the digital subcarriers to provide the digital subcarrierswith desired spectral shapes. The pulse shape filters 470 may beconfigurable, adjustable, and/or programmable such that the frequencybandwidths are configurable. One or more filter control signals 483 maybe used to adjust, configure, and/or program the pulse shape filters470.

FIG. 16 illustrates a diagram of another exemplary digital signalprocessor 310 c of an exemplary transmitter 212 which may be used toconfigure the power gain to digital subcarriers SC1-SC4. The digitalsubcarriers SC1-SC4 may be processed through the pulse shape filters470. Then, one or more digital multiplier 478, for example, digitalmultipliers 478-1 to 478-4 corresponding to the digital subcarriersSC1-SC4, may be used to control the level of electrical power of thedigital subcarriers SC1-SC4. The digital subcarriers SC1-SC4 may then beprocessed through the multiplexer 482, before proceeding to the IFFTcomponent 490 and the take last component 495, as previously describedin relation to FIG. 3.

FIG. 17 illustrates a diagram of another exemplary digital signalprocessor 310 d of an exemplary transmitter 212 which may be used toconfigure the power gain to digital subcarriers SC1-SC4. One or moredigital multiplier 478, for example, digital multipliers 478-1 to 478-4corresponding to the digital subcarriers SC1-SC4, may be used to controlthe level of power of the digital subcarriers SC1-SC4. The digitalsubcarriers SC1-SC4 may then be processed through other components ofthe digital signal processor 310 d, such as the replicator 460, thepulse shape filters 470, and the multiplexer 482, before proceeding tothe IFFT component 490 and the take last component 495, as previouslydescribed in relation to FIG. 3.

As previously described, the digital signal processor 310 a, 310 b, 310c, 310 d may be part of the transmitter 212. The digital signalprocessor 310 a, 310 b, 310 c, 310 d may receive a plurality ofindependent data streams 352-1 to 352-4 and supply outputs based on theplurality of independent data streams 352-1 to 352-4. The outputs mayinclude two or more digital subcarriers, such as a first digitalsubcarrier having a first frequency bandwidth and a second digitalsubcarrier having a second frequency bandwidth different than the firstfrequency bandwidth. The digital signal processor 310 a, 310 b, 310 c,310 d may configure one or more of the digital subcarriers to controlthe electrical power levels of one or more of the digital subcarriers.For example, the digital signal processor 310 a, 310 b, 310 c, 310 d mayconfigure a first digital subcarrier to have a first level of electricalpower and a second digital subcarrier to have a second level ofelectrical power different than the first level of electrical power.

As previously discussed with regard to FIG. 2, the transmitter 212 mayalso include one or more digital-to-analog converter 320 configured toconvert the outputs of the digital signal processor 310 a, 310 b, 310 c,310 d to voltage signal outputs; the laser 330 configured to output anoptical light beam; and the modulator 340. The modulator 340 isconfigured to modulate the optical light beam, based on the voltagesignal outputs, to output a modulated optical signal including aplurality of optical subcarriers based on the outputs of the digitalsignal processor 310 a, 310 b, 310 c, 310 d. The plurality of opticalsubcarriers may carry data indicative of the plurality of independentdata streams, respectively or in combination. The plurality of opticalsubcarriers each has a respective bandwidth. For example, a first one ofthe plurality of optical subcarriers has a first optical bandwidth and asecond one of the plurality of optical subcarriers has a second opticalbandwidth different than the first optical bandwidth.

Further, one or more of the plurality of the optical subcarriers mayhave an optical power level different than one or more of other ones ofthe optical subcarriers, as a result of the power levels of one or moreof the respective digital subcarriers. For example, the first one of theplurality of optical subcarriers may have a first level of optical powerand the second one of the plurality of optical subcarriers may have asecond level of optical power different than the first level of opticalpower, corresponding to the electrical power levels of the respectivedigital subcarriers.

In use, the digital signal processor 310 a, 310 b, 310 c, 310 d may beused to adjust the shape of the digital subcarriers and correspondingoptical subcarriers. In one implementation, the digital signal processor310 a, 310 b, 310 c, 310 d may be used to adjust the shape of opticalsubcarriers for use with systems having legacy Optical Power Monitoringalgorithms. For example, in previous systems, optical carriers such asthe exemplary carrier λ₁ depicted in FIG. 18, may have been degraded atthe outer edges of the optical bandwidth of the carrier λ₁ by roll-offfrom one or more filter. Because of this degradation, some Optical PowerMonitoring algorithms are designed to expect optical carriers to havehigher power in a center region of the optical bandwidth than at theouter edges of the optical bandwidth of the optical carrier. Suchsystems may search for peak power near the center region of the opticalbandwidth of optical carriers.

In contrast, the optical subcarriers SC1-SC4 depicted in the carrier λ₂in FIG. 19 are not degraded. This may result in some Optical PowerMonitoring algorithms not recognizing the optical subcarriers SC1-SC4,since there is no roll-off of power from the center region of theoptical bandwidth than at the outer edges of the optical bandwidth ofthe optical subcarriers SC1-SC4.

As illustrated in FIG. 20, through control of the optical power of theindividual optical subcarriers SC1-SC4, as described above, in carrierλ₂′ the optical subcarriers SC1′ and SC4′ in the outer edges of theoptical bandwidth may be reduced in power (or left at a lower power) andthe optical subcarriers SC2′ and SC3′ in the center region of theoptical bandwidth may be provided more power gain (or left at a higherpower than the optical subcarriers SC1′ and SC4′) such that the opticalsubcarriers SC2′ and SC3′ in the center region have a higher power thanthe optical subcarriers SC1′ and SC4′ in the outer edges. This shapingof the optical subcarriers in the optical carrier λ₂′ mimics the shapeof previous system optical carriers λ₁ sufficiently to permit the legacyOptical Power Monitoring algorithms, without modification, to recognizethe coherent carrier λ₂′ and perform, for example, Power Controlbalancing functions.

Through the use of the digital signal processor 310 a, 310 b, 310 c, 310d to shape the spectral channel through shaping the digital subcarriers,a variety of additional performance improvements can be made tocompensate not only for impairments, but also to compensate for commonDWDM deployment scenarios where the required power varies depending oncharacteristics of the transmission paths of the optical subcarriersthrough the optical network. For example, different transmission pathsmay have a varied number of fiber splitters and power combiners, and/ordifferent distances/lengths of the transmission paths.

For example, FIGS. 21 and 22 illustrate an exemplary optical network 200f having a hub 920 a, a plurality of edge nodes (illustrated forexplanatory purposes as Edge 1 through Edge 4), links 230, and one ormore power splitters 922 a (such as 922 a-1, 922 a-2, and 922 a-3). Thehub 920 a may have a receiver 226 and may have one or more transmitter212 having a digital signal processor 310 a, 310 b, 310 c, 310 d asdescribed in FIGS. 14-17. The hub 920 a may output a plurality ofoptical subcarriers, such as, for example, SC1-SC4, to the edge nodesEdge 1-Edge 4. The power splitters 922 a may supply a power splitportion of the plurality of optical subcarriers to one or more edgenodes Edge 1-Edge 4. Each edge node Edge 1-Edge 4 may comprise areceiver 226 that may receive one or more or all the optical subcarriersSC1-SC4 and that may output less than all of the data from the clientdata streams of all of the optical subcarriers. Each edge node Edge1-Edge 4 may further comprise a transmitter 212.

As shown in FIG. 21, if the hub 920 a transmits the optical subcarriersSC1-SC4 at the same optical power level (that is, the optical powerlevel of the optical subcarrier SC1 is the same as the optical powerlevel of the optical subcarriers SC2, SC3, and SC4), the differingcharacteristics of the transmission paths between the hub 920 a and eachedge node Edge 1-Edge 4, results in varied optical power levels of theoptical subcarriers SC1′-SC4′ when received at the edge nodes Edge1-Edge 4. Such variable power loss may be due to characteristics of thetransmission paths such as, but not limited to, fiber types, fiberdistances, type of equipment/optical components within the paths, andnumber of equipment/optical components within the path.

In this example, the optical subcarriers pass through three powersplitters 922 a-1, 922 a-2, and 922 a-3 in the transmission path fromthe hub 920 a to the edge nodes Edge 3 and Edge 4, while the opticalsubcarriers pass through two power splitters 922 a-1, 922 a-2 in thetransmission path from the hub 920 a to the edge node Edge 2, and theoptical subcarriers pass through one power splitter 922 a-1 in thetransmission path from the hub 920 a to the edge node Edge 1.

If the power splitters 922 a are 50/50 splitters, then from the powersplitter 922 a, the optical subcarriers continue along two paths withhalf of the light continuing through a first of the two paths and theother half of the light continuing through the a second of the twopaths. Both paths may contain all the optical subcarriers but eachcarrier is at half of the power before the split. This representsroughly a 3 dB loss in the optical power of the carrier. As one exampleapplied to the optical network 200 f, if the optical power per carrierat the hub 920 a is 15 dBm, the receive power per carrier at each edgenode Edge 1-Edge 4 is as follows:

Edge 1=12 dBm;

Edge 2=9 dBm;

Edge 3=6 dBm;

Edge 4=6 dBm.

As illustrated in FIG. 22, a relative delta in the power of thesubcarriers may be used when the hub 920 a is transmitting to severaledge nodes Edge 1-Edge 4, when the desired transmission powerrequirement is different, in order to achieve a desired receiver powerat each edge node Edge 1-Edge 4 to achieve optimal or a desired minimumperformance level. The digital signal processor 310 a, 310 b, 310 c, 310d of the transmitter 212 of the hub 920 a may be used to configure thepower level of the digital subcarriers, and thus of the opticalsubcarriers output from the transmitter 212 such that the opticalsubcarriers have the desired receive power at the edge nodes Edge 1-Edge4. In the example optical network 200 f, if the desired optical powerreceived per optical subcarrier at each edge node Edge 1-Edge 4 is 6dBm, then the hub 920 a may transmit each subcarrier SC1-SC4 with thefollowing optical power in order to obtain the desired power at the edgenodes Edge 1-Edge 4:

SC1=9 dBm;

SC2=12 dBm;

SC3=15 dBm;

SC4=15 dBm.

As another example, FIGS. 23 and 24 illustrate an exemplary opticalnetwork 200 g having a hub 920 a, a plurality of edge nodes (illustratedfor explanatory purposes as Edge 1 through Edge 4), links 230, and oneor more power splitters 922 a (such as 922 a-1, 922 a-2, and 922 a-3).The hub 920 a may have a receiver 226 and a transmitter 212. Each edgenode Edge 1-Edge 4 may comprise a receiver 226 and a transmitter 212having a digital signal processor 310 a, 310 b, 310 c, 310 d asdescribed in FIGS. 14-17. The edge nodes Edge 1-Edge 4 may output one ormore optical subcarriers, such as, for example, SC1-SC4, to the hub 920a. The power splitters 922 a may supply a power split portion of theplurality of optical subcarriers to the hub 920 a.

As shown in FIG. 23, if the edge nodes Edge 1-Edge 4 transmit theoptical subcarriers SC1-SC4 at the same optical power level (that is,the optical power level of the optical subcarrier SC1 is the same as theoptical power level of the optical subcarriers SC2, SC3, and SC4), thediffering characteristics of the transmission paths between each edgenode Edge 1-Edge 4 and the hub 920 a results in in varied optical powerlevels of the optical subcarriers SC1′-SC4′ at the hub 920 a. Forexample, the optical subcarriers pass through three power splitters 922a-1, 922 a-2, and 922 a-3 in the transmission path from the edge nodesEdge 3 and Edge 4 to the hub 920 a, while the optical subcarrier(s) passthrough two power splitters 922 a-1, 922 a-2 in the transmission pathfrom the edge node Edge 2 to the hub 920 a, and the opticalsubcarrier(s) only pass through one power splitter 922 a-1 in thetransmission path from the edge node Edge 1 to the hub 920 a.

If the power splitters 922 a are 50/50 splitters, then from each powersplitter 922 a, the optical subcarriers continue along two paths withhalf of the light continuing through a first of the two paths and theother half of the light continuing through the a second of the twopaths. Both paths contain all the optical subcarriers but each carrieris at half of the power before the split. This represents roughly a 3 dBloss in the optical power of the carrier. As one example applied to theoptical network 200 f, if the optical power per carrier is 15 dBm, thereceive power per carrier at the hub 920 a is as follows:

Receiver Power at Hub 920 a from Edge 1=12 dBm;

Receiver Power at Hub 920 a from Edge 2=9 dBm;

Receiver Power at Hub 920 a from Edge 3=6 dBm;

Receiver Power at Hub 920 a from Edge 4=6 dBm.

As illustrated in FIG. 24A, a relative delta in the power of thesubcarriers may be used when the edge nodes Edge 1-Edge 4 aretransmitting to the hub 920 a, when the desired transmission powerrequirement is different, in order to achieve a desired receiver powerat the hub 920 a to achieve optimal or a desired minimum performancelevel. The digital signal processor 310 a, 310 b, 310 c, 310 d of thetransmitters 212 of the edge nodes Edge 1-Edge 4 may be used toconfigure the electrical power level of the digital subcarriers, andthus the optical power level of the optical subcarriers output from thetransmitter 212 such that the optical subcarriers have the desiredreceive power at the hub 920 a. In the example optical network 200 g, ifthe desired optical power received per optical subcarrier at the hub 920a is 6 dBm, then the edge nodes Edge 1-Edge 4 may transmit therespective optical subcarriers SC1-SC4 with the following optical powerin order to obtain the desired power at the hub 920 a:

SC1=9 dBm;

SC2=12 dBm;

SC3=15 dBm;

SC4=15 dBm.

As illustrated in FIG. 24B, in one implementation one or more variableoptical attenuators 928 in the transmission path can be configured tocontrol the optical power level of the optical subcarriers, such thatthe optical subcarriers have the desired receive power at the hub 920 a.The variable optical attenuator(s) 928 may be component(s) of one ormore optical components in the transmission path. In one implementation,the variable optical attenuator(s) 928 may be included in of one or moreintegrated VOA/Multiplexer 923-1, 923-2, and 923-3, as shown in FIG.24B.

In another example, FIGS. 25 and 26 illustrate an exemplary opticalnetwork 200 h having an edge node Edge 1, a first hub 920 a-1, a firsttransmission path 924-1 between the edge node Edge 1 and the first hub920 a-1, a plurality of optical components 926 in the first transmissionpath between the edge node Edge 1 and the first hub 920 a-1, a secondhub 920 a-2, and a second transmission path 924-2 between the edge nodeEdge 1 and the second hub 920 a-1. Each hub 920 a-1, 920 a-2 maycomprise a receiver 226 and a transmitter 212. The edge node Edge 1 maycomprise a receiver 226 and a transmitter 212 having a digital signalprocessor 310 a, 310 b, 310 c, 310 d as described in FIGS. 14-17.

The edge node Edge 1 may output one or more optical subcarriers, suchas, for example, SC1-SC4, to the first and second hubs 920 a-1, 920 a-2.All of the optical subcarriers SC1-SC4 may be transmitted to each of thefirst and second hub 920 a-1, 920 a-2 and one of or more of the opticalsubcarriers may be ignored by one or both of the first and second hubs920 a-1, 920 a-2, and/or one or more of the optical subcarriers may befiltered before reaching the first or second hub 920 a-1, 920 a-2. Orfewer than all of the subcarriers may be transmitted to the first andsecond hub 920 a-1, 920 a-2 from the edge node Edge 1. For example, thefirst and second optical subcarriers SC1, SC2 may be transmitted to thefirst hub 920 a-1 and the third and fourth optical subcarriers may betransmitted to the second hub 920 a-2.

In the exemplary optical network 200 h, the first transmission path924-1 between the edge node Edge 1 and the first hub 920 a-1 hasdifferent characteristics than the second transmission path 924-2between the edge node Edge 1 and the second hub 920 a-2. In general, thelevel of optical power of respective optical subcarriers may be based atleast in part on one or more characteristics of the first transmissionpath 924-a and the second transmission path 924-2.

For example, the first transmission path 924-1 may have a first lengthand the second transmission path 924-2 may have a second length shorterthan the first length. Additionally, or alternately, a larger number ofoptical components 926 may be in the first transmission path 924-1 thanin the second transmission path 924-2. It will be understood that othercharacteristics of the first transmission path 924-1 may also bedifferent than characteristics of the second transmission path 924-2.For example, the types of filters in the optical components 926 and/ortheir widths and/or the number of filters in the transmission paths 924through the optical network 200 h that the optical subcarrier will take,as well as the number and locations of receivers 226, and the capacityof such receivers 226, may determine required receive power of theoptical subcarriers.

As shown in FIG. 25, the different characteristics of the first andsecond transmission paths 924-1, 924-2 may result in different opticalpower of the optical subcarriers SC1′-SC2′ received at the first hub 920a-1 versus the power of the optical subcarriers SC3′-SC4′ received atthe second hub 920 a-2. For example, the optical power of the opticalsubcarriers SC1′-SC2′ received at the first hub 920 a-1 may be less thanthe optical power of the optical subcarriers SC3′-SC4′ received at thesecond hub 920 a-2 because the length of the first transmission path924-1 is longer than the length of the second transmission path 924-2and there are more optical components in the first transmission path924-1 than in the second transmission path 924-2.

As illustrated in FIG. 26, a relative delta in the optical power of theoptical subcarriers may be used when the edge node Edge 1 transmits tothe first and second hubs 920 a-1, 920 a-2, when the desiredtransmission power requirement is different, in order to achieve adesired receiver power at the first hub 920 a-1 and the second hub 920a-2 to achieve optimal or a desired minimum performance level. Thedigital signal processor 310 a, 310 b, 310 c, 310 d of the transmitter212 of the edge node Edge 1 may be used to configure the electricalpower level of the digital subcarriers, and thus of the optical powerlevel of the optical subcarriers output from the transmitter 212 suchthat the optical subcarriers SC1-SC2 have the desired receive power atthe first hub 920 a-1 and the optical subcarriers SC3-SC4 have thedesired receive power at the second hub 920 a-2. In one non-exclusiveexample, average power may be maintained at the first hub 920 a-1 andthe second hub 920 a-2 by increasing the optical power of the opticalsubcarriers SC1-SC2 and reducing the optical power of the remainingoptical subcarriers SC3-SC4 at the transmitter 212 of the edge node Edge1, such as by utilizing the digital multipliers 478 in the digitalsignal processor 310 a, 310 b, 310 c, 310 d.

In one aspect of the present invention, a control feedback loop from thereceiver 226 of the edge node Edge 1-Edge 4 or hub 920, 920 a that isreceiving the optical subcarriers to the transmitter 212 of the edgenode Edge 1-Edge 4 or hub 920, 920 a that is transmitting the opticalsubcarriers, may be used to adjust the optical power of individualoptical subcarriers at the transmitter 212, to improve performance basedon ongoing measurements of the performance at the receiver 226.

Relative optical power adjustments to the optical subcarriers may beused to improve overall performance at the receiver(s) 226. Usingmultiple optical subcarriers and having each optical subcarrierdemodulated independently allows independent measures of performance“Q”. The ability to measure the Q for respective optical subcarriers andthe ability to independently control the relative optical power ofrespective optical subcarriers enables an implementation of a feedbackloop to increase or decrease the optical power of respective opticalsubcarriers to achieve an overall optimal Q. This may include tradingoff excess Q on one or more optical subcarriers to those opticalsubcarriers that require additional Q. This may be due to differentmodulations used per optical subcarrier where each has a different OSNRor Q requirement or could be due to varied impairments due to differentrouting, for example.

The adjusted optical power of the optical subcarrier(s) may be used toovercome variable distances, a varied number of splitters, and/or otherimpairments or requirements in the transmission path 924 or route orreceiver 226. Each optical subcarrier from each transmitter 212 may belaunching at a different and/or relative optical power such that whenthe optical subcarriers reach the location of the receiver 226, theoptical power is at a target optical power level to achieve the desiredOSNR for each optical subcarrier servicing the Hub/Edge pair.

The feedback loop may be implemented in several ways to determine theperformance of the optical subcarriers and to provide information and/orinstructions to the transmitter 212 of the optical subcarriers from thereceiver 226 of the optical subcarriers and to adjust parameters of theoptical subcarriers. One such parameter is the optical power of theoptical subcarriers, which may be adjusted through the digitalmultipliers 478, for example.

In one implementation of a feedback loop, as illustrated in FIG. 27, anoptical network, such as optical network 200 i, transmitting opticalsubcarriers SC1-SC4 from the transmitter 212 of the hub 920 a to thereceiver 226 of the edge node Edge 1, may further comprise an opticaltap 940, a tunable filter 942, a receiver-side photodiode 944, areceiver-side processor or control circuit 946, an Optical ServiceChannel (OSC) transmitter 948, a combiner or multiplexer 950, ademultiplexer 952, a transmitter-side photodiode 954, and atransmitter-side processor or control circuit 956.

The optical tap 940 may split a portion of the light of one or more ofthe optical subcarriers to the tunable filter 942 at, or before theoptical subcarriers enter, the receiver 226 of the Edge 1. The tunablefilter 942 may scan the light spectrum of the optical subcarriers andtransmit the scanned light to the receiver-side photodiode 944, whichmay convert the light into electrical signals. The electrical signalsmay be detected by the receiver-side processor or control circuit 946,which may track the amount of current and corresponding optical power ofthe optical subcarriers (that is, the amount of light detected). Thereceiver-side processor or control circuit 946 may determine theadjustments needed to be made to the optical subcarriers. The OpticalService Channel (OSC) transmitter 948 may transmit informationindicative of the adjustments needed to be made to the opticalsubcarriers. The OSC transmitter 948 may transmit the information to thetransmitter 212 of the hub 920 a in a feedback optical signal that is ata different wavelength than the optical subcarriers. For example, theOSC transmitter 948 may transmit the information at 1310 nanometers.Once combined at the combiner or multiplexer 950, the feedback opticalsignal may be sent to the transmitter 212.

At or before the transmitter 212 of the hub 920 a, the feedback opticalsignal may be filtered at the demultiplexer 952 and sent to thetransmitter-side photodiode 954. The transmitter-side photodiode 954 mayconvert the light of the feedback optical signal into electrical signalsand transmit the electrical signals to the transmitter-side processor orcontrol circuit 956. The transmitter-side processor or control circuit956 may interpret the feedback information and output signals to adjustgains of the digital subcarriers in the digital signal processor 310 ofthe transmitter 212, such as through controlling the digital multipliers478, for example, thereby adjusting the optical power of the opticalsubcarriers.

In one implementation, as illustrated in FIGS. 28 and 29, an opticalnetwork, such as optical network 200 f transmitting optical subcarriersSC1-SC4 from the hub 920 a to the edge node Edge 1 (as shown, forexample, in FIGS. 21-22), may transmit feedback information as to theperformance of, and/or adjustment needed to the optical power of theoptical subcarriers, modulation type, spacing increase or decrease fromadjacent subcarriers, further spectral shaping of the subcarrier,roll-off, and so on, from the receiving end (here, the edge node Edge1).

In one implementation, the feedback information may be transmitted usinga sideband generator process. In such a system, the transmitter 212 ofthe edge node Edge 1 may impose on the high frequency optical signal(such as that carrying the subcarriers SC as shown in FIG. 29) a lowfrequency optical signal “control channel” CC (as shown in FIG. 29) tocreate a side band signal to carry feedback information regarding theoptical subcarriers' power performance that was received at the receiver226 of the edge node Edge 1. Additionally, the low frequency signal maybe used to carry feedback information for both the in-phase andquadrature components, and may be used for both the X polarization andthe Y polarization. The out-of-band signals may be added to the outputsof the digital signal processor 310 of the transmitter 212 which issupplied to the DACs 320. The hub 920 a may filter the side band signalfrom the optical transmission to the hub 920 a from the edge node Edge 1(such as with filter 958) and process the side band signal to use toadjust the electrical power levels (that is, adjust the gain) of thedigital subcarriers and the corresponding optical power of the opticalsubcarriers transmitted from the transmitter 212 of the hub 920 a, aspreviously explained. In one implementation, the hub 920 a may furthercomprise a processor or control circuit 956. The processor or controlcircuit 956 may interpret the feedback information and output signals toadjust gains of the digital subcarriers in the digital signal processor310 of the transmitter 212, such as through controlling the digitalmultipliers 478, for example, thereby adjusting the optical power of theoptical subcarriers.

In one implementation, the digital signal processor 310 in thetransmitter 310 may further comprise an electrical filter or filteringcircuit that may filter the feedback information.

In one implementation, as illustrated in FIG. 30, the feedbackinformation may be carried from the receiving end in the header of aframe carried by the optical signals from the transmitter 212 of theedge node Edge 1. This method may use the header to uniquely identifythe Edge and Hub messages along with instructions to, for example,increase and/or decrease the optical power, such that the optical powerlevels of one or more of the plurality of the optical subcarriers may bebased on the data of the feedback information in the header.

Although these examples show power related information in the feedbackinformation, additionally or alternatively, the method may be used toexchange different type of messages.

FIG. 31A illustrates another example of a receiver consistent with thepresent disclosure. The receiver shown in FIG. 31A is similar to thatshown in FIG. 6. In FIG. 31A, however, a filter circuit 986 is coupledor connected to an output of detectors 630-1. Although one suchconnection is shown in FIG. 31A, it is understood that connections mayalso be made to another output of detectors 630-1 and/or to one or bothoutputs of detectors 630-2. Filter circuit 986 may be, for example, aband-pass filter or a low pass filter to provide an electrical signalcorresponding to the low frequency or tone signal carried by thesideband signal discuss above. Filter circuit 986 may provide the tonesignal to a control circuit 990, which may include demodulationcircuitry, for example, to provide data or extract data from the tonesignal.

Control circuit 990 may provide an output to the transmit DSP notedabove, and, based on such output, optical power levels, for example, ofthe subcarriers may be adjusted. For example, the output of controlcircuit 990 may include information for setting or adjusting the gainvalues input to the multiplier circuits discussed above.

In one implementation, as illustrated in FIG. 31B, the power of theoptical subcarriers may be monitored through monitoring the digitalsubcarriers in the digital signal processor 650 a of the receiver 226.In this example, after the Fourier transform component 810, eachsubcarrier may be assigned a group of registers or memories, each ofwhich stores a frequency component of a particular subcarrier at thedemultiplexing component 815. For example, subcarrier SC1 may beassociated with 512 of the bins (that is, the converted time domain intofrequency domain). A processor or circuit 819 may determine the energylevel (power) of the subcarrier by calculating the square of theabsolute value of each frequency bin at the output of the demultiplexingcomponent 815 associated with a particular subcarrier, and taking thesum of those squares. The sum corresponds to the power of thesubcarrier. That power feedback information may be sent to thetransmitter 212 of the hub 920 a (such as via the methods previouslydescribed) to be used to adjust the optical power of the opticalsubcarriers.

It will be understood that the above described systems for feedback totransmitters 212 transmitting optical carriers may also be used wherethe edge node(s) are transmitting the optical subcarrier(s) to thehub(s) 920 a.

Accordingly, as noted above, a simplified and less expensive transmittermay be realized consistent with the present disclosure in which a laserand modulator may be employed to generate multiple subcarriers, wherebyeach of which may be detected and the client data associated therewithmay be output from receivers provided at different locations in anoptical network, for example. Improved network flexibility can thereforebe achieved.

Other embodiments will be apparent to those skilled in the art fromconsideration of the specification. It is intended that thespecification and examples be considered as exemplary only, with a truescope and spirit of the invention being indicated by the followingclaims.

CONCLUSION

Conventionally, a plurality of lasers and modulators were necessary tocreate optical signals to carry a plurality of data streams. Inaccordance with the present disclosure, a plurality of subcarriers isgenerated from a single laser to carry a plurality of data streams, suchthat a lesser number of lasers and modulators are needed across anoptical network.

The foregoing description provides illustration and description, but isnot intended to be exhaustive or to limit the inventive concepts to theprecise form disclosed. Modifications and variations are possible inlight of the above teachings or may be acquired from practice of themethodologies set forth in the present disclosure.

Even though particular combinations of features are recited in theclaims and/or disclosed in the specification, these combinations are notintended to limit the disclosure. In fact, many of these features may becombined in ways not specifically recited in the claims and/or disclosedin the specification. Although each dependent claim listed below maydirectly depend on only one other claim, the disclosure includes eachdependent claim in combination with every other claim in the claim set.

No element, act, or instruction used in the present application shouldbe construed as critical or essential to the invention unless explicitlydescribed as such outside of the preferred embodiment. Further, thephrase “based on” is intended to mean “based, at least in part, on”unless explicitly stated otherwise.

What is claimed is:
 1. A transmitter, comprising: a digital signalprocessor operable to receive a plurality of independent data streams,the digital signal processor including: Fast Fourier Transform circuitryoperable to provide frequency domain data based on signals indicative ofthe plurality of independent data streams, a plurality of memoriesoperable to store the frequency domain data, the digital signalprocessor being operable to provide outputs indicative of the frequencydomain data, the outputs of the digital signal processor includingdigital signals associated with a first frequency bandwidth and a secondfrequency bandwidth, the second frequency bandwidth being different thanthe first frequency bandwidth; digital-to-analog converter circuitryconfigured to convert the outputs of the digital signal processor tovoltage signal outputs; a laser configured to output an optical signal;and a modulator configured to modulate the optical signal, based on thevoltage signal outputs, to output a modulated optical signal including aplurality of optical subcarriers, wherein a first one of the pluralityof optical subcarriers carries data indicative of a first one of theplurality of independent data streams, and a second one of the pluralityof optical subcarriers carries data indicative of a second one of theplurality of independent data streams, wherein the first one of theplurality of optical subcarriers has a first optical bandwidth and thesecond one of the plurality of optical subcarriers has a second opticalbandwidth different than the first optical bandwidth, and the first oneof the plurality of optical subcarriers has a first level of opticalpower and the second one of the plurality of optical subcarriers has asecond level of optical power different than the first level of opticalpower, wherein the frequency domain data includes a plurality of bits, afrequency gap between the first one of the plurality of opticalsubcarriers and a second one of the plurality of optical subcarriersbeing variable based on values of the plurality of bits.
 2. Thetransmitter of claim 1, wherein the digital signal processor comprises aplurality of digital multipliers corresponding to the plurality ofindependent data streams, the plurality of digital multipliers supplyingmultiplier outputs based on multiplier inputs indicative of thefrequency domain data such that the power levels of the opticalsubcarriers are based on the multiplier outputs.
 3. The transmitter ofclaim 2, wherein the multiplier outputs are adjustable based on one ormore control signal such that the first and second levels of opticalpower are adjustable based on said one or more control signal.
 4. Thetransmitter of claim 3, wherein a third one of the plurality of opticalsubcarriers has a third optical bandwidth different than the firstoptical bandwidth, wherein the third one of the plurality of opticalsubcarriers has a third level of optical power different than the firstlevel of optical power, wherein the first level of optical power isgreater than the second and third levels of optical power, and whereinthe first optical bandwidth is in between the second optical bandwidthand the third optical bandwidth.
 5. The transmitter of claim 2, whereinthe digital signal processor comprises a plurality of pulse shapefilters corresponding to the plurality of independent data streams, thefirst and second optical bandwidths of the first and second digitalsubcarriers being based on outputs of the plurality of pulse shapefilters.
 6. The transmitter of claim 5, wherein each of the plurality ofpulse shape filters is adjustable based on one or more control signalsuch that the first and second optical bandwidths are adjustable.
 7. Thetransmitter of claim 1, wherein the first level of optical power of thefirst on of the plurality of optical subcarriers is based on one or morecharacteristics of a first transmission path carrying the first one ofthe plurality of optical subcarriers, and the second level of opticalpower of the second one of the plurality of optical subcarriers is basedon one or more characteristics of a second transmission path carryingthe second one of the plurality of optical subcarriers.
 8. Thetransmitter of claim 1, wherein the digital signal processor comprises aplurality of digital multipliers supplying electrical signals such thatthe first and second optical power levels are based on the electricalsignals output from the plurality of digital multipliers.
 9. Thetransmitter of claim 1, wherein the digital signal processor comprises aplurality of pulse shape filters, the first and second opticalbandwidths of the first and second digital subcarriers being based onoutputs of the plurality of pulse shape filters.